The movie starts out showing the downtown area of Ogden Marsh, Iowa. It is destroyed and cars are on fire. Then the screen fades away to reveal the same shot only it is your normal small town downtown area and in the corner it says *Two days earlier*
We are introduced to Becca (Danielle Panabaker), she is apparently a receptionist in for Dr. Judy Dutton (Radha Mitchell) , the towns only doctor who is in the early stages of pregnancy and the wife of the town Sheriff David. She tells Dr. Dutton that she just got a call and her aunt is in town and needs to leave early. Dr. Dutton is not buying it and instead says "Tell your boyfriend Scotty that he will just have to watch the baseball game alone tonight, I am gonna need you to stay late". Becca stutters and realizes she has been caught but to her relief Judy says "Oh I understand, enjoy the game, get outta here". Becca says thank you and leaves.
At the town baseball game, it seems everyone has shown up for, we meet David Dutton (Timothy Olyphant) , the town Sheriff. He is talking to his deputy Russell (Joe Anderson). While the local high school teams play, they notice a local walking out to the field with a shotgun. David recognizes him and orders all the teams into their dugouts and approaches him. The man is dazed looking and has a bloody nose. David tries to get the man to drop his firearm but the man (whom David knows well, and by name) just stares at him before finally raising his weapon to fire on David. In self-defense, David shoots the man in the head, killing him instantly. The horrified crowd can only watch in horror.
Later at the local funeral home, David is telling the owner that he assumes that the man he shot was drunk because he had a history of being "the town drunk". It is the only way he can dismiss his odd behavior. The mortician tells him it will take a few days to get the results and he will let him know. In the lobby of the funeral home, he sees a woman and a teenage boy, the mortician says it’s probably not a good time to approach them but David does anyway. He walks up to the woman and boy and says "I am so sorry". The young boy looks very angry but the mother holds him back. The woman says "What was he doing out there?". David says "I don't know, but he didn't respond to me so I just assume he was drinking". The woman immediately says back "that is impossible, he has been sober for months, are you sure he was drunk?" David replies "Well, we will know in a few days. David returns to the baseball field and sees the local Principal Ben (Larry Cedar) sitting in the bleachers. David walks up to him and tries to talk to him but Ben just stares straight ahead. David finally gets his attention and Ben says "Don't worry, the kids are resilient. They will be ok". David asks if he is ok and he says yes and David leaves.
Back at Dr. Dutton's office, a woman comes in with her husband and young son (probably 8 or 9) and tells Judy "Can you check out my husband? He is not normal". Judy takes him into an examining room and starts checking his vitals and is asking the man questions but he is not responding. Finally he says "Oh she just worries too much, I am ok". To which Dr. Dutton replies "Are you hurting anywhere? Any discomfort?" to which the man replies "Oh she just worries too much, I am ok". She gives him a funny look and sends him on his way. Outside, she tells the wife that he appears to be ok, his vitals are normal but she wants him to go for a CT Scan on Monday just to make sure. They all say their goodbyes and the family leaves.
Later that night, we see the same wife at their home in the country. She sees out in their barn that one of their machines is running full tilt. She tells her son to stay there and she goes to investigate. She gets to the barn and sees that their large mower is running and she looks around for her husband, calling out his name but there is no reply. She gets into the mower and sees nobody is there. She then hears her son screaming from the house and she runs to it. She finds her son and he says "Its Daddy, he has a knife". She grabs her son and runs upstairs to hide in a closet. She can see through the keyhole that he is coming towards them. He stops in front of the door and instead of opening it, he locks the door from the outside. She starts yelling his name and trying to get the door open but she has no luck. The husband then starts dumping gasoline down the stairs and out the front door. He then strikes a match and drops in onto the trail of fuel. Burning his wife and small son alive in their home. David gets a call at home (its early am like 4 or 5 I would guess) and says he is on his way. He and his wife arrive at the still smoldering house and you can see the husband just calmly sitting on a truck bed and whistling (very creepy). Judy says "What have you done?" he doesn't reply and keeps whistling.
Down at the jailhouse, they have the husband in custody (its one of those old time jail cells where you can see the inmates from the front door, all open). Deputy Russell is looking at the husband and asks David "How long has he been playing statue?" since he is just standing there, blank faced. David replies "That is the same look that man gave me on the baseball field the other day...the exact look". David gets a call from the mortician with the blood results from the man he shot. It is revealed that the man he killed had no alcohol in his system at all. David is stunned to hear this news and is more worried than ever now.
Three hunters are out in the woody marsh apparently hunting ducks when they notice a skydiving parachute in the tree next to them. One of them pulls on the ropes to find a deceased pilot. They jump back and call for help. When David and a detective arrive, the detective says the body has probably been there for 3 months by the way it looks (it was actually 3 days). He tells the hunters to put their guns away until spring because it’s not legal to hunt right now. They argue but say ok. He comes back out to the same place, only this time with Russell and another man running the boat. He said that someone reported a few days ago that they heard a loud crash so to be on the lookout for a small plane to go with the pilot they found. After a few minutes, David instructs the man to turn the boat motor off. Russell asks if he can see the airplane they are looking for and David replies "It is right underneath us". The screen pans out to reveal not a small plane but a very large plane that had settled in the lake below them.
David starts to think that maybe the water could have been contaminated by this plane because he knows that their towns water supply comes from that river. He gets a map and traces from where the water starts flowing into the towns drinking water and realizes the first house it goes through is the man he shot at the baseball field, the second in line? The man that just murdered his family and is now in their custody. Russell starts to get worried because he notices on that map that his house is only a few away from there. David assures him that he will be fine. David and Russell drive out to the mayor’s house and ask that the water be turned off so that they can investigate. The Mayor tells them that there is no way he will do that since they live in a farming town and it is almost Spring. If they turn off the water, the families wont be able to harvest.
David and Russell drive out to the city water supply and turn off the water themselves. Russell is worried about his job but David assures him that he believes that is the least of their worries right now. They notice that their inmate is laying apparently dead in his cell now. Russell tries to get his keys out and go inside but David stops him. They both kneel down and the husband jumps out after them. There is blood all over him and his cell from him slowing dying from the contamination. They leave him be. David walks outside and notices that there is seemingly nobody in town and for some reason, his cell phone is not getting a signal. He tells Russell "We are in big trouble". David sees about a block down that there is a black SUV that seems out of place. The windows are all tinted out so he can’t see who or what is inside. He starts walking that way, then starts running. When he gets a few hundred feet from it, it takes off fast, spinning tires and all.
David goes home and tells his wife to pack her bags and go to her Mom's for a few days and he would come for her and that he cant leave now because he is the Sheriff. She resists reminding him that she is the town’s only doctor and while they are talking, she stops David and says "Someone is outside". He goes to investigate and is apprehended along with his wife and taken away. They get on the bus and Russell is already on it so they sit with him. This is definitely military, tanks full camo and all. They are taken to the local high school where it is total chaos. There are school buses full of the town people and they are rushing them all through a contamination area. They are taking everyone's temperature and if they find you are running a fever, you are taken to a different area. If you are not, you are taken to an outside kennel so to speak. David makes it through and is not running a fever so he is given a bracelet and they scan it. His wife Judy however is and they pull her away from David and take her a different way. They also take Russell. They try to struggle but it is no use. David tries to tell them that she is pregnant and has been running a fever all month but it does no good. They show David being taken to waiting buses. He sees a man he knows and asks him where his wife is, the man tells him that they took her as well. The other man starts to get on the waiting bus and David says he can just leave his wife behind. As that happens, a truck full of "healthy" people drive through the kennel outside and the people just start shooting everyone. The military calls this a huge security breach and orders the school evacuated immediately, just leaving everyone there to die.
David knows he can’t go after these people unarmed so he goes back to the jail to get a gun. When he gets back there, he notices that the husband is for sure dead now, propped up in the corner. It looks like the bled to death out of his head. Hard to be totally sure, they never really address it. Russell says he is really worried now that he might have it because he was running a fever. David brushes it off and says they gotta get to the safe zone they are taking everyone so they can get help and get out of town. David walks outside and hears a noise coming from the funeral home. He walks in and it is deserted until he notices that one of the sheets is moving. When he pulls it back, he notices it is the mortician’s helper and he is alive but his eyes are sewn open and his mouth is sewn shut. David grabs some scissors and cuts his mouth open and the man immediately says "Behind you!". He turns around in time to get hit in the head with a pole from the mortician. He now has the crazies. He attacks David with a saw, trying to cut him but David overpowers him and the mortician gets killed by his own saw. They show a large truck stop type gas station on the outskirts of town and it is swarming with military as well as the buses and transport trailers you saw earlier that were transporting the "healthy" out of town. David and Russell return to the High School to save Judy.
Judy is strapped to a hospital bed surrounded by dozens of locals that are also strapped to beds. The military had tied them up seemingly to keep them from hurting people that are not infected. Everyone around her is giggling and smiling loudly (they have the crazies) she notices that her receptionist Becca is on a bed across from her. Judy tells her they will be ok just to hang on. They hear a noise coming and Judy tells Becca to be quiet. You see a pitchfork dragging along the ground with blood dripping off of it. The person dragging it is the high school principal Ben. He looks stunned and out of it (he has the crazies). He walks up to a man that is strapped to a bed and is laughing uncontrollably and takes the pitchfork and stabs him in the chest (pretty gross). To this action, Becca and Judy start freaking out and try to wiggle out of their straps. Ben then walks to a woman that is also strapped down and laughing and stabs her several times. He then walks over to Becca who is crying and begging for her life. Ben is just staring blankly at her and starts to raise his pitchfork again, only this time to stab her (she doesn't have the crazies, neither does Judy). Just as he is about to stab Becca, Judy screams out to get his attention. He looks her way and starts walking towards her now. She starts thinking that this might have been a bad idea and starts to scream and wiggle harder to get out of the straps. Ben approaches her and starts to raise his pitchfork again and just as he is about to stab her, a shot hits him right in the head, killing him instantly. As he drops it is revealed that the shooter was David and Russell and they are there to rescue them.
Now it is David, Judy, Becca and Russell. They know they need a car but there are no cars in the area so they decide to walk to find something. They start searching the cars on the street downtown but they are all either on fire or not working. They notice a truck and Russell goes to inspect it and says there are keys in it. David however notices that there is blood dripping out of the tailgate and looks in to see about 10 dead bodies. David tells Russell to back off from the truck and hide. You can hear men talking and around a corner comes a man running for his life. The three hunters (from earlier) are chasing him. They shoot him and drag his body to the truck and put him in the back and drive away. Apparently they are out now hunting for people. They are walking through the night to get to David & Judy’s house to get his car. On their way, they notice Becca's boyfriend's house (Scotty from the beginning) and Becca starts running towards it. When they get there, they find Scotty but he has a shotgun on them, thinking they are crazies. They figure out that none of them are infected so they decide to help each other. They hear a noise and David instructs everyone into the barn and they ask Scotty where his family is and he says his Mom is still in the house gathering supplies. The noise they heard was a military tank and truck pulling up to Scotty’s' house. They start to go towards the house and Scotty tries to go help his Mom but David holds him back. When Scotty hears his Mom screaming, he runs out of the barn yelling "I am not sick, I am ok!". They are dragging his Mom out the front door. They shoot Scotty and when his Mom runs out to him, they shoot her too. Then a man walks up with a blowtorch and sets their bodies on fire. The military men then instruct the soldiers to sweep the entire property for others. David and Russell hear this and tell Judy and Becca to hide in the back of the barn. A soldier comes into the barn and David knocks him out. They drag him to the back of the barn and take off his mask and ask what is going on. The soldier tells them that he doesn't know but they have instructions to keep their masks on and to kill everyone that doesn't have one on. David tells him that they are not sick and just trying to get to help and if he tells the others that they are there, he will kill him. Another soldier comes in and asks him if he found anything and the solider says its all clear. The military leave and the four of them set out again for David’s home.
David says he has a old car at their house that they can use so they start walking that way. They get there by morning and David tells his wife to pack up what they can and to hurry. Meanwhile Russell and him prepare the car. Judy goes upstairs to pack and walks by the baby room that her and her husband have been preparing for their new baby's arrival. She walks into the room to get one last look and behind her you can see a Crazie (it is the woman who's husband was shot in the beginning of the movie at the ballpark). Then they show David who is looking for his wife. He enters the baby's room and notices that she is tied to the rocking chair. She tries to scream and warn him but her mouth was gagged. David is jumped by the young boy (who's father he killed at the ballpark), the boy is trying to strangle him. David is trying to reach his gun (it was knocked out of his hand from the initial attack from the boy). As he almost reaches the gun, he is stabbed in the hand by the mother and she grabs the gun. The mother (she and her son have the crazies bad!) informs her son that she thinks this is the same gun that he used to kill his father. She aims for Judy and David tries to get her attention by saying "Yeah, I shot him, the lousy town drunk, kill me, not her". The young boy gets up only to be shot by Russell through the window from outside. The mother lunges for David but is stabbed in the neck from the same knife that the woman used to pin his hand down.
They all get into the car and drive off.
The four of them are driving when Judy says they need to find a road that they wont find them on, David yells at her and asks her to tell him what road they can drive on that the helicopters wont see them on. She just says she is trying to help and David apologizes. Meanwhile, Becca starts to cough and Russell freaks out and says "You are not getting sick are you? Because if you are, we don't want you in this car". David tells him to relax and actually has to tell a few times before he finally does stop talking about it. While they are driving, Becca notices a military helicopter. It flies over them and then turns around and heads back towards them. David quickly drives into one of those coin-operated car washes that pull your car through to clean it. When they get inside it, the helicopter leaves. They think they are ok but all of a sudden you can see a man standing at the end of the wash (another Crazie) and the car wash starts to pull the old police car through it and of course, the car decides its not gonna start. The Crazie is trying to break into the car to kill them and busts out the front windshield. Judy grabs his head and starts bashing it on the dash and he is finally killed when David shoots him. They are finally ok and the car starts. David puts the car in drive and jams on the gas pedal to get out of there. On their way out, the Crazie jumps back up and tries to grab someone through the back glass. He is shot but one of the ropes from the car wash gets tangled around Becca's neck and pulls her out the back glass, hanging her. The car is out of the car wash and David, Judy and Russell jump out of the car to save her but it is too late, she is dead. They are inside the car wash and crying over her death when the car they were in suddenly explodes and a helicopter flies off. If they had been in the car still, they would have all been dead.
David, Judy and Russell start walking to try to get to the truck stop and Russell starts acting strange. They notice a station wagon on one side of the highway and on the other side is Russell's police truck. Russell walks over to his truck to try to find supplies. They see a black SUV heading their way on the road and David tells them that he is going to take this truck from the driver and to get down. David draws his gun and points it at the SUV when Russell pops out and throws spike strips onto the road making the SUV flip several times. David asks him what he did that for and Russell didn't really have an answer. David tells Russell to stay back that he was going to get some answers. An old retired military man gets out of the destroyed SUV and David tells him he is the town Sheriff and wants answers. The man informs him that they made a mistake. The airplane was carrying a biological weapon called "Trixie" to a location in Texas to be destroyed but it crashed, contaminating their town’s water supply and they have to contain it. As the man starts to explain more, Russell shoots the man in the head. David tells him he just wanted to talk to the man and Russell replies "You did talk". Judy tells David that she knows Russell is sick now. Russell sets down his gun to search the SUV and David takes it. They start to walk again and Russell tells David he wants his gun back and David says "Its ok, I will carry it for a while" to which Russell takes out a smaller gun and demands it. He forces David and Judy to walk ahead of him. After a while, David tells Judy that he is going to confront Russell because it’s their only chance. David turns around and tells Russell to drop the gun. Russell has that same dazed look on his face and his nose starts to bleed. He suddenly seems to realize what is going on and says "I am not right am I?" to David. David says "No, you are not". Russell starts to get sad and says "Can I just walk with you guys for a while, please?". They agree and start to walk again.
They come upon a roadblock and realize they cannot cross. Russell, realizing he is dead anyway, says he will distract them while they cross the roadblock and get to the truck stop. He runs out and of course is shot dead, but meanwhile David and Judy are able to get past them to continue to the truck stop. They arrive at the truck stop and it is empty. David assures Judy that it was filled with people and buses just the previous day. They don't know what to do. David tells Judy to wait outside and he goes inside to get supplies and look for a car. David notices a truck in the repair part of the truck stop and starts looking for keys and gathering water and clothes. Judy is outside and can see the trailers they used to transport the "healthy" to the truck stop to get them on busses out of town. She looks inside one and is horrified to see that the trucks are full of dead people. They have all been shot and burned alive. They were not transporting them to safety after all. They are exterminating everyone. David finds her and takes her back inside and you can see in the kitchen of the restaurant that one of the hunters from earlier is in there (he has the crazies). He starts chasing after her but she hides in a meat locker (full of dead people). David is sighted by the other hunter (he also has the crazies) and he quickly tries to get Judy into the truck to escape. David is yanked out of the truck by one of the hunters while another one attacks Judy. Judy just shoots one in the head and starts the truck. David fights the other one and throws oil on him and set him on fire. David jumps into the truck and they take off.
While they are driving out of town, they can hear on one of the walkie-talkies they found a countdown. It starts at 30 and Judy says "What happens when it gets to zero?" David says, "I don't know"....then he pushes the gas down as hard as he can. They are barreling down the road whiles the countdown is trickling away. Judy is watching out the back window and when it gets to zero David says "Well??" and Judy says "Nothing"...then all of a sudden a nuclear bomb is dropped on the town behind them. The force from the blast throws the truck off the road. They are ok and step out onto the road to see the large mushroom cloud that used to be their town. They start walking towards Grand Rapids. As they are walking towards the town, you can see a military type scan of them and the area they are in and it shows the town they are walking to and it says "Initiate containment procedure", indicating that the town they think they are going to get help in is also going to be destroyed by the military since they think David and Judy have the crazies too and simply escaped.
Midway through the credits, you see a local news broadcast that says the blast everyone heard the other day was simply a power plant that exploded and not anything military....
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