NOTE: This spoiler was sent in by Brad
The movie begins with a blue meteor flying through outer space and then plummets toward earth. Cut to the Department of Defense: Northeast Airspace Security where one of the employees is having an argument on the phone about missiles. Since he's caught up, he doesn't notice the warning saying something is coming towards Earth.
In the next scene we see a boy Josh (Austyn Myers) looking through his telescope, now noticing a red object coming near him. Meteorites then start to crash in his room, one landing in the fishbowl. The mom Gina (Elizabeth Banks) startled, comes to the room to see what's going on and the boy explains the situation, but she doesn't believe him and leaves the room. The boy then runs to his fishbowl and the meteorite starts to suck the water out of it.
Three Months Later.
The comet crashes to the Earth, near the Statue of Liberty. We then see Dave (Eddie Murphy) trying to walk normal. The Police Department notices the "fireball" and has Dooley (Scott Caan) and Knox (Mike O' Malley) check it out. We then go back to New York City. Dave is copying all his surroundings and eventually gets hit by Gina and Josh's car. Dave walks to an alleyway with an injured foot. Then a door in his ear opens and little people climb down to his foot to help fix it. They then go the head where mini-Dave is to give a status report.
Somehow Gina finds him and tries to get him help, but notices his foot is all better.
Gina then takes him back to her apartment where Dave sings, cooks, and kicks their cat. We then realize that Gina's husband Frank died and it is only she and the son. Suddenly, NO. 3 (Gabrielle Union) notices the orb in a picture (The meteorite that landed in Josh's fishbowl). The picture was from one of Josh's science fair projects. Dave then leaves to "Locate the boy."
Dave encounters an electronics store where headphones create an earthquake in his head. Then he encounters a clothing store where he crashes through all the racks.
At Josh's school, a bully teases him about the meteorite and then takes it. Dave walks in and fakes being a substitute teacher so he could talk to Josh. Josh says the bully took the meteorite but he would be at the deli. They both finally arrive at the deli, but the bully isn't there. Suddenly, two thieves walk in, but Dave kicks their butt. Both go back to Josh and Gina's house. They play video games for a while until Gina comes home.
Back at the crash site, a mold is made of the crash site because Dave landed face first. So a clay mold of Dave's face comes through. They go to the station and shows the head chief, but he thinks it's nonsense. But, Dooley insists it's an alien. He makes copies of the print out of the face.
Dave, Josh, and Gina all go to the carnival and ride some rides, which make the people in Dave's spin as well but they like it. The rest of the night, Dave does a hot-dog eating contest (obviously winning). But, then Rich (the bully) is at the fair and Dave shakes the meteorite out of him.
Afterwards Dave plays a ball toss game, where the ball hits his head and knocks him out. But soon enough he's back to normal at the doctor's so they start to walk out and a guy at the desk notices him from the wanted flyer.
It's Gina's birthday so they go to a salsa restaurant where Dave has his first cocktail and dances. Meanwhile, No.3 starts to hit on mini-Dave but it doesn't seem to work. All of a sudden the policemen, Knox and Dooley, come and take Dave to the station.
The two officers try to question him, but he doesn't say anything. Then, No.2 (Ed Helms) in Dave's head says he's taking over the ship. No.3 agrees and handcuffs mini-Dave. They don't realize that the speaker is on and the two officers are hearing everything and leave to discuss. In, the meantime, Dave takes out his blasters and shoots around the jail till' he escape.
No.3 leaves, to save mini-Dave. They both get caught and are placed in the nostrils. No.2 sneezes and they are shot out of Dave. People get close to smooshing them, but they don't. Eventually mini-Dave and No.3 grab on a windshield and get launched on big-Dave.
No.2 is heading toward the ocean. The orb is used to suck the water out of the oceans, and the world. He finally gets there and is about to throw the orb when Mini-Dave overrides the system in another part of the body. Dave accidentally flips and the orb falls in the water.
Inside of Dave, mini-Dave is put back in control. They can't save the Earth without being stuck there.
Everyone decides to take the risk.
Dave gets the orb and saves the day. But, the sheriff comes and is going to shoot him. Dave doesn't have enough power to protect himself. Josh grabs one of the sheriff's tasers and shoots Dave -- repowering him. Before they shoot, big-Dave's tongue comes out and mini-Dave walks out and shocks everyone.
He apologizes to everyone for the havoc spread. Then No.3 walks out and mini-Dave says he feels love to her. They all go back inside and start to lift-off but a net captures him. The FBI comes but suddenly a foot comes off of Dave and it shoots to outer space. Dave and all the crew are aboard and safe.
In the ship, No.3 and mini-Dave kiss. They finally get home.