As the film opens we see falling blue lights, like flares, raining down on Los Angeles at night time, evenly spaced over the terrain. Then we see young couple Jarrod (Eric Balfour) and Elaine (Scottie Thompson) being woken by blue lights outside the window shining through the slates in the blinds. Elaine thinks it is morning, and she gets up and goes to the bathroom to throw up. When she returns to bed the room starts shaking and Jarrod goes to the window to lift the blinds and find out what the ruckus is. An anguished shout from the next room stops him, and Jarrod goes out to find Denise (Crystal Reed) crying that the lights took Ray (Neil Hopkins). The blinds are up here, and the door is open, and as Jarrod looks at the blue light shining in the room blue/black veins start to grow all over his eyes, cheekbones and shoulders, and his eyes go mottled-opaque. Terry (Donald Faison) and Candice (Brittany Daniel) are also woken, and go into the living room where the lights are. Jarrod starts to move mindlessly towards the light.
15 hours earlier. Jarrod and Elaine arrive by plane from New York to visit Terry, who is a childhood friend of Jarrod and is now doing extremely well for himself by working for a special effects company, for his birthday. Terry has them met at the airport by a limo and once they arrive at the apartment Terry shows them their room, introduces them to Candice, his girlfriend and Denise his PA (personal assistant), shows them around, and they go to the building swimming pool to party and get drunk. Elaine, Candice and Denise look on at their men getting drunk and acting crazy like two overgrown teenagers. They notice Homeland Security helicopters flying over their building and across the nearby marina. Terry checks the news on his portable iPad but it appears there is nothing out of the ordinary.
That evening, everyone celebrates Terry's birthday by holding a big party at his penthouse apartment. At one point the building manager, Oliver (David Zayas), comes and asks them to keep the noise down as there have been complaints.
Ray, a business associate of Terry's, lets the cat out of the bag that Terry wants Jarrod to move to Los Angeles and work with him, doing visual effects. Jarrod does not seem keen but Elaine is angry and upset. Later on, she tells Jarrod that she is pregnant, upsetting him; he says that he is not ready for that and she agrees. After they make up, Jarrod and Elaine find out that Terry is cheating on Candice with Denise. Elaine wants to tell Candice, but Jarrod, wanting to protect his friend, tells her to stay silent.
Day 1: 4:27 a.m. Opening where the movie began, we see the blue lights falling from the sky, one of them landing in the courtyard outside the high-rise apartment building, and Ray being taken, this time from Denise's point of view. After they drag Jarrod away from the lights the veins go away, although that's clearly a painful process, and he can't see properly while it's dissipating. Then, the blue flares take off back into the night sky.
Terry and Jarrod go up to the roof to see what is going on. Terry takes his revolver and Jarrod takes his camera. They meet Terry's elderly neighbor Walt (Robin Gammell) in the hall with his dog, and tell him to return to his apartment. Back in the apartment, the ladies try to find information to what is going on, but all the TV channels have no signal, and all news stations show empty studio sets. Elaine tries calling her mother in New York, but only gets her voice mail.
On the roof, Jarrod lets the security door close behind him so the guys are trapped on the roof. It is dawn, and they see huge clouds rolling in to Los Angeles, with flickers of blue lightning, and the blue flare lights return back to the ground. Then, descending from the clouds is an armada of large alien spaceships of various shapes and sizes, all over the city. The spaceships suck up clouds of dust, and Jarrod uses his Canon EOS camera to shoot pics; they realize the 'clouds' are actually thousands of screaming humans being sucked into each ship by a vacuum in the blue lights. Then they see dozens of smaller flying alien drones emerging from the ships and flying all over the city. A flying alien drone appears over the edge of the roof and the guys are nearly caught by it's ray-like blue light. Terry shoots the door handle so they can get back into the building, to no avail, but Elaine arrives and opens it from the inside and saves the guys. Elaine looks in the blue light from the flying drone alien and gets veiny, but Jarrod carries her back to the apartment with Terry.
Everyone looks at the images and is horrified. Candice looks at the rest of the images on the camera, and someone has taken shots of Terry and Denise having sex. She is pissed off, but stays silent.
Looking through the telescope, the crew sees that there are no lights, ships or aliens over the ocean. Terry's plan is to drive to the marina, get in his boat, and get away from the city. Elaine tries to persuade everyone to stay in the apartment and wait until someone comes, but she soon relents and agrees to go with Terry's plan.
Terry goes to Walt's apartment to get his keys so they can have two cars. While talking to Walt, a flying alien drone hovers outside the window and sends tentacles in to search the room. Walt's persistently barking dog gives Walt and Terry away, and Walt (and the dog) are grabbed and sucked up by the flying drone. Terry gets away, with the Mercedes keys. He gets the others from his apartment and they all take the elevator to the underground parking garage.
Terry and Denise take Terry's Ferrari, while Candice drives Elaine and Jarrod in Walt's Merc. On the way out they meet a bickering couple, Colin (J. Paul Boehmer) and Jen (Tanya Newbould), packing their car and also attempting to flee the building. Terry leaves the car park first, but the car crushed by a stomping alien standing over 20-feet tall. Denise is killed, but Terry falls out of the car and tries to get away, ineffectively shooting the "stompy" tanker alien with his weapon. Jarrod leaps out and pulls Terry to safety, but the stomping tanker shoots out a long multi-tongued appendage and sucks Terry back to it's grasping claws and seemingly consumes/eats him. Elaine pulls Jarrod back in to the car, and Candice backs it up while stomping alien tries to get in to the car park. While fleeing back into the garage they encounter a multi-blue eyed, squid-like alien life form (resembling a cross between the aliens in 'Independence Day' and the bio-mechanical flying robots from the 'Matrix' movies). It takes Colin into its tentacles after paralyzing him with its own blue light. It corners the rest of the group and affects Jarrod with its blue light. Then suddenly the building manager, Oliver, slams into it with an SUV. Oliver and Jen pull Colin out covered in black goo and gasping for air. However the squid alien is not dead, and a tentacle sucks onto Colin's head and pulls out his brain, brain stem, and part of his spinal column and puts the brain into its own head... as if recharging itself with the human brain like a new battery. Oliver has the keys to the building so he hurriedly opens an internal security door and the rest escape through it.
The group runs out of the garage and past the swimming pool, making for the back gate entrance of the building. But the two-legged alien stomper ambushes them, shooting three sticky tongue-things at them and stomping everywhere. He snags Jen and engulfs her. The rest discover a second stomping tanker heading from the other side of the building. Trapped between the two alien tankers, Oliver breaks a glass door and they head back inside and climb back up the fire stairs to Terry's apartment to regroup.
The trembling and immature Jarrod is upset that he let Terry go and didn't save him. Elaine is upset that no one listened to her and they made a pointless effort to escape from the building that cost lives. Candice takes the time to light herself a cigarette, but Elaine asks Candice not to smoke, because she is pregnant. Elaine is worried that the veiny-thing blue-light has permanently affected their bodies and what that might do to her baby. Jarrod pulls up his shirt and sees that he has veiny-things on his abdomen that aren't going away. Oliver and Jarrod barricade the front door and keep watch while the women sleep. They hang out there a for the rest of the day. That evening, through the telescope, the crew see the military begin to fight back in the streets with tanker and hydra aliens. A few hours later, the water is cut off.
The next morning (Day 2), the four survivors (Jarrod, Elaine, Oliver, and Candice) debate over what to do next. Jarrod wants to make another attempt to get to the marina to find Terry's motorboat to escape. Oliver is against this as is Elaine and Candice, reminding him that even if they did get to the boat and escape from Los Angeles, they ask Jarrod where would they go for they must consider that this alien invasion is happening all over the world since there has been no news on the TV, radio, or Internet since yesterday morning. Jarrod stubbornly doesn't seem to care and just wants to get out of the building and away from there... despite no plan at how to get away or where to go.
The group's debate is interrupted when they hear the sound of flying jets overhead. Looking out of the window, with Oliver manning the telescope and the rest watching on the flat-screen TV set, they see that all of the other alien ships have departed, save for one big one hovering over downtown L.A. The US Air Force has launched a counter-attack against the aliens. They watch a large squadron of several dozen unmanned Predator drones, armed with air-to-air sidewinder missiles, escorting a handful of unmanned Stealth bomber drones, flying towards the large hovering alien spaceship which is presumably the mother ship. Hundreds of alien drones fly out of the alien ship and engage the Predator and Stealth drones in a huge aerial battle (resembling hornets or wasps protecting their hive from a enemy swarm of other insects). Many Predator, Stealth and alien drones are destroyed; the group notices that the flying alien 'Matrix-esq' drones do not appear to have any weapons such as laser cannons or missiles, but they seem to crash themselves into the unmanned aircraft with little or no regard for their own well being.
Most of the Predator drones and Stealth bomber drones are destroyed in the dogfight, until a single surviving Stealth bomber gets through the carnage and fires a missile at the alien ship before it is destroyed as well. The missile hits and explodes inside the large alien ship.... in a massive nuclear explosion, creating a massive shock wave. Out of the mushroom cloud, the alien ship is blown apart and crashes into the ground. Everyone hugs and laughs with joy at the burning hulk. Then... looking through the telescope, Jarrod sees the ruins of the ship as it glows with a blue light. Thousands of drone, tanker, and squid aliens crawl out and begin to swarm all over the city. As the smoke from the mushroom cloud clears, the group watches with disbelief as the alien spaceship slowly rises back into the air and all of the broken-off pieces rise with it and slowly re-attach themselves... self-regenerating. A couple of the blinds fall down and Oliver and Candice tape up sheets over the windows with duct tape so the blue lights from the alien ship will not affect them.
Then, the group see a military helicopter deposit soldiers on a nearby building rooftop. Jarrod decides to take Elaine and go to the roof and get rescued by the military. Oliver tries to stop them but Jarrod gets very violent and veiny: he says he feels powerful from the light, and he will not leave without his family. Elaine says she trusts him, and they leave.
Candice sees the blue light of the large regenerating ship through the telescope and goes veiny. She opens the door and walks out and gets taken by a squid alien that is climbing up the side of the building. Oliver tries to stop her, but fails, and barely escapes himself. The squid alien that consumes Candice is blown apart by a rocket fired by the soldiers on the roof of the nearby building.
On the roof, Jarrod and Elaine see that the soldiers are from a U.S. Navy fleet that has arrived off-shore. In the distance near the ruins of downtown L.A., the alien spaceship, surrounded by blue light, continues to slowly repair itself. They witness another huge aerial battle as U.S. Navy jet fighters appear and battle stomping tankers and flying alien drones, with little success. A military helicopter that Jarrod and Elaine try to wave down gets tongued and destroyed by another tanker alien that scales the other building. The tanker is blown down from the building by a rocket fired by the soldiers, but it gets back up and begins to climb up the side of the building towards the apartment.
With the windows and shades now blown out and nowhere to run or hide, Oliver gives it all up as hopeless. He turns on the gas stove and lets it accumulate. When the tanker alien reaches the apartment and tries to tentacle him, he flicks a lighter and blows himself and the alien up.
When Jarrod and Elaine see Oliver's fireball from the rooftop, they realize it's clear and hopeless as the aliens are unstoppable.
Jarrod and Elaine turn around to go back downstairs, but there is a squid alien in the stairwell blocking their path which bursts through the fire door at them. Jarrod tries to fight it off with a fire axe while Elaine escapes. When Jarrod chops off one of the squid alien's tentacles, it picks the severed piece up and re-attaches it. The squid alien stabs Jarrod in his right leg which enables it to try hook another one of it's tentacles to his head as it apparently prepares to consume his brain too. As he writhes on the rooftop, Elaine grabs the axe and hacks the alien's brain out. But even without it's brain, the squid alien still won't die and it turns to concentrate on her; while it is distracted Jarrod bashes its head in with a cinder-block, then his fists, then he starts pulling black gooey brain matter and membrane out with his bare hands in slow-motion apparently killing it for good.
Elaine and Jarrod are still on the rooftop surrounded by more flying drones, squid and hulking tanker aliens and they climb higher trying to find any safe place. They are confronted by a burned tanker alien (the same one that Oliver attempted to destroy by blowing up the apartment), burned to a crisp. Just then, a F-22 fighter jet, hit by another flying alien drone, crashes into the tanker and takes it out just before it gets Jarrod and Elaine, who end up lying on the helipad at the very top of the building as the large alien ship, now having completely repaired itself, slowly cruises over the building. Many more alien ships return and begin releasing their blue lights and vacuuming up the few surviving people in the city. Exhausted and seeing that the aliens have totally defeated the military and all of the U.S. Navy ships off shore are on fire and sinking, Elaine and Jarrod can run no longer. Giving up as hopeless, they both look up at the hovering spaceship and go veiny. They kiss and hold each other as they are sucked up into the ship.
Next, there is a montage of shots of global cites all in ruins with alien ships over them (New York, London, Hong Kong, Los Angeles, etc.). There appears to be no way of stopping the alien invasion. It is very clear at this point that humanity is doomed. The aliens have won.
Day 3. Elaine wakes up in the alien ship inside a dark chamber, covered in black tarry goo. There are dead people and tentacles everywhere, the former having their brains sucked out by the latter. The brains move through tubes further into the craft. The headless bodies are dropped into a pool of liquid far below. Elaine crawls through bloodied and gooey dead human bodies looking for Jarrod. Just as she finds him his brain is sucked out by a tentacled machine. She is upset. As she is about to have her brain sucked out a tentacle realizes Elaine is pregnant. She is sucked into a larger tube.
The sucked-out brains come to a place where new, sloth-like creatures are made; they're just waiting for a human brain. Most brains are blue-green colored, but one arrives that is orange/red (from the timing we are led to believe this is Jarrod's). The alien entity which receives it convulses and is overtaken with Jarrod's consciousness. It is upset at being an alien in a world of goo and rampages a bit.
Elaine is spat out into a different chamber full of other pregnant women and is covered with tentacles which are presumably going to do unspeakably horrid things to her, as the other women are screaming in terror. Jarrod-alien hears Elaine's voice and crashes through the wall, fighting off the tentacles and saving her. He touches her stomach, we hear a rapid heartbeat, he strokes her face with his new, three fingered paw. Elaine recognizes the alien as Jarrod. Jarrod-Alien rises up triumphantly, standing guard over his love. He picks her up and holds her as more alien tentacles converge on him.
On this cliffhanger note, the movie ends with a series of still images between the closing credits that depict the new "Jarrod" protecting Elaine and their unborn child from other aliens. Eventually alien "Jarrod" defeats them, picks his wife up, and runs off with her into the bowels of the alien spaceship.