The movie begins with the camera focusing on an electronic clock that shows three o'clock in the morning and the date September 11th, 2001. The alarm clock is turned off just a minute before it is supposed to go off by John McLoughlin (Nicholas Cage). John gets up to get ready quietly without waking his wife, but his wife is just lying still, with her eyes open.
John leaves for work, and when he puts on his hat, we understand that he is a cop, port police officer to be exact. The day seems like any other day, the routines, the city that comes to life in the morning, and at the station, we are introduced to a few more young officers in their lockers getting dressed. The officers are Will Jimeno (Michael Pena), Dominick Pezzulo (Jay Hernandez) and a few more insignificant ones.
During role call, John assigns individual officers to their locations, and they are off to work. Will and Dominick chat a bit before they go their own way to do their walks. Will sees little petty crimes that are about to happen, like two guys pointing at a purse a woman is wearing and following her, and a man picking on a tourist to help her carry her bags. All this is interrupted when a really loud roar and a shadow of a plane goes by.
In the next scene, we see offices shake after the loud boom sound that vibrates the entire city. People gather to watch the news on TV, and that is when they all realize one of the World Trade Center towers was hit by a plane. We can see the people were a little amazed, thinking it was just a freak accident, making fun of the idiot that flew a plane into a tower, not realizing this was actually done by terrorists.
John gathers up a few guys, and says that they have to shift their duties to the World Trade Center, where help is needed. A couple of the officers get on the bus and head towards the towers. On the bus, officers begin to call their loved ones and friends, talking about the accident. Most calls are not going through anymore, since the entire city was overloading. One of the officers in the back puts his phone down and said "I heard another plane hit the second tower.¨ The rest of the officers just shrugged it off as it was just a rumor.
When they arrive at the scene, all the smiles and laughter stopped. The site is really depressing and stunning, with ashes and papers and smoke all over the place. Visibility is getting low, and John asks the group who is willing to go in there with him. Most of the officers just stand there, still amazed by the unrealistic sight, while Will, Dominick and two more officers volunteer to go with John.
John was a little disappointed at the rest of the guys, but he immediately starts telling the plans to the group. Radio and all other form of communication is down, even talking to each other had to be yelled out, since there are people screaming from all over, bodies are falling from the sky, and the fire was crackling extremely loud. John used to work in the WTC, so he knows the buildings inside out. John knows that there are a few oxygen tanks and masks and suits in one of the smaller buildings, which was what they had to do first. They are joined by another officer, who actually was bleeding from his head, and on their way to the gear, they pass by numerous police and firemen that are heading into the towers. They exchange some pleasantries and wished each other good luck. John says him and his team will be right up after they get the gear.
The moment John and his crew get the gear and are heading towards one of the main towers, they see a lot of civilians in shock and are supported by each other as they walk out of the building. Will is pushing the heavy cart that carries all the gear, while one of the officers offered to take over (thus forcing Will to switch places with the officer).
Just then, rumbling noises get louder, and John sees that the injured civilians outside the building are being crushed by ashes and debris. John realizes that the entire building is coming down, and the entire team started to run towards an exit within the building. The officer that switched places with Will is blocked by the large cart, and is buried alive with two other officers, while John, Will and Dominick make it into the door, and the screen turns black and silence.
With a little light shining through the ten stories (at least) of debris, we see the lights coincidentally shine right on the three survivors. John is trapped on his side at a much lower position then Will and Dominick. Will is pinned face-up from his chest down, while Dominick fortunately only got a few scratches and bruises from the debris. Will was crying for help, and asked that Dominick help lift the huge concrete off his chest. The concrete is too heavy for Dominick to lift, so he suggests that he get out and call for help. But Will starts to cry and beg Dominick not to leave him, and help lift the huge concrete. Even though it was humanly impossible, we see Dominick agree and try to lift the debris with a steel metal.
The debris is too fragile, and things start to fall apart once again, with more rumbling noises and more things falling around. John is then hit on the side and he lets out a loud excruciating scream while more debris falls and things go quiet again.
When more lights shines through, John and Will are in their exact position, but Dominick is completely pinned against two huge concretes. Dominick is spitting blood and is in extreme pain, and he asks John if he could get a "38¨ (which was a code for a break or something, but if you know guns, it is a .38 caliber that cops use). John said he's allowed to, and Dominick takes out his gun and is going to use to it on himself. He fired into nowhere with his last breathe, and died. Will begins to regret, because he was the one that begged Dominick to stay. The two lay there for hours, talking, trying to get each other to stay awake.
In another scene, we see that John's wife, Donna (Maria Bello) is worried and watching the news. She seems to know for sure that John has gone into the buildings to do his job. No one in the station is able to confirm anything, since all communication is down for awhile, and hundreds of city workers were still missing.
Another scene shows Will's wife, Allison (Maggie Gyllenhaal) pregnant and worried that her husband did not call. She's also accompanied by her and her husband's family in the house, waiting for a call.
In both scenes, officers were seen pulling up to their houses, not to deliver the bad news, but the confirmation that both Will and John went into the building, and have not heard a thing.
In one more scene, we see retired Marine Sergeant Dave Karnes (Michael Shannon) somewhere in New Jersey watching the news. He proceeds to dig up his old marine uniform and get dressed and geared up and heads towards New York City to help.
In the meantime, we see Will talking to John about wives and families and life. John has four kids, and he is actually having trouble in his marriage. Will is expecting his second child, and he is still arguing with his wife what to name their daughter (the wife wants Olivia, but he wants Melissa). Will also finds a steel pipe that was right on top of him, with some water dripping down, while drinking the water, he accidentally rattles the pipe, which created a loud snap sound. John told Will to keep doing that, since rescuers might be able to hear them.
Both survivors took us in a journey to their flashbacks, their love for their wives and kids, and the same with the wives visualizing their husbands with the kids. Will had a really funny scene, when he tells John that he just saw Jesus in his head, and Jesus is holding a water bottle, walking towards him. John is in a lot more pain than Will is, because his knees are crushed into each other. At least Will was able to move his arms around, and he keeps on snapping the pipe in hope of someone to hear them.
In the meantime, the search is called off for the night, because it was too hard to see, and they did not believe there will be any survivors. This is when Sergeant Karnes, the marine arrives and begins to search on his own, disregarding orders. During his search, he runs into another rescuer, Marine Sergeant Thomas (William Mapother), who also disregarded orders and joined Karnes to search for survivors. They hear Will snapping the pipe at one point, and they called out to rescuers. All of a sudden, every single man that was in the area comes to the rescue.
Two men go down the tiny little spaces between the debris to get to Will, only understanding that Will is with another person, for which they only saw Will and Dominick. One of the rescuer coveres the body of Dominick with his jacket. The rescuers used some kind of inflating bags to finally lift the concrete off Will, and are able to carry Will out safely. But then they were reminded by Will that there is another person down there, and they told him that Dominick is dead already. But then they realize there is another person, John, trapped in a much lower level of where Will was retrieved.
So the rescue continues, and as more hours go by, it seems John is about to give up. But the image of his wife keeps popping up, as if she was right there with him, telling him to hang on. Then the rescuers finally get to John, and safely deliver him out on a stretcher, with people clapping and congratulating each other.
In the hospital, after the wives of Will and John are informed of them being alive, but then to be disappointed again knowing that they are still trying to get them out. They finally received confirmation that they got out safely and are in the hospital already. When Donna finally sees John, John said to her, "you kept me alive." While Will is having dust and dirt sucked out of his mouth, he yells to his wife he wants his daughter to be named Olivia (her choice) and she wants her to be named Melissa (his choice), and he was taken into surgery.
A year later, that we see both John and Will along with families and friends in a welcome back party. Both guys are limping around, surrounded by wives and kids and friends, and we see Will and his newborn girl.
Nicholas Cage narrates in the final scene, "The world saw evil that day, sure we did, but we also saw what good could come through in a time like this.¨
With the scene fade to black, a couple facts about that day and the people were stated.
John was in and out of surgery for numerous hours, and had to be in a medically-induced coma to fight through the pain, and retired after this.
Will is still an active officer of the port authority.
Hundreds of officers and firemen and volunteers were trapped inside the towers. But only 20 of them survived and were rescued. John and Will were number 18 and 19.
Retired Sergeant Karnes returned to active duty and served two terms in Iraq.