The movie begins with an airplane flying to Moscow; onboard many of the passengers are asleep as a stewardess does her rounds checking on passenger needs. Sean (Emile Hirsch) is playing a video game on his cell phone. The stewardess tells him to shutoff his phone, yet he questions her about the supposed need as he doubts that a phone could make the plane fall out of the sky. His friend Ben (Max Minghella) is embarrassed by antics, but does not tell him to stop. Sean asks her if she agrees, just keep her arms crossed. She looks at him and keeps her arms crossed and smiles. The lights go out suddenly due to an electrical short, and the two guys are startled. The plane lands safely at the airport in Moscow.
As they exit they are trying to get ready for a presentation; Ben notices a stain on Sean’s suit and uses a sharpie marker to cover it up. Sean and Ben are a pair of software developers, and they are trying to market a social media program that would make it easy for people to find parties, events, and friends all around the world. Sean mentions he found a hot Russian nightclub called Zvezda where he hopes to get drunk and meet hot models. Ben tests the app and finds a number of American ladies who are in Moscow. Sean comments that they did not travel this far to meet Americans; if they wanted to do so they could go to Applebee’s.
They enter the meeting but are greeted curtly by their Russian associate Skyler (Joel Kinnaman); he states they are no longer needed, and that should leave. They notice Skyler is demonstrating their social media software to a number of Russian investors, and accuse him of stealing their project. Skyler tells them that it is how business is done in Moscow. Ben and Sean are pissed off but leave after security arrives to walk them out.
Natalie (Olivia Thirlby) and Anne (Rachael Taylor) are walking around Moscow talking pics and marveling at how beautiful the city is at night. They mention the blog that Ben and Sean setup and comment that they look cute. They take a picture of themselves in front of the Kremlin. Ben and Sean find Zvezda and talk about the possibility of suing Skyler, but they are skeptical that Russia law would agree with them. They see Skyler at the club and confront him; he tells them once again that they are naïve and act like sheep to his wolf.
Sean gets drinks and mentions no society exists with out alcohol and religion. Ben uses his phone app and finds that Natalie and Anne are in the club. They impress them by saying they invented the app that the ladies were using, and the ladies ask if they are internet millionaires. They say they are internet billionaires. Ben developed the app while Sean is the one who finds the exciting places to party. They enjoy drinks and shares stories of what brought them to Moscow; they then take a photo together. Suddenly the lights go out in the club.
They go outside and are in a crowd of surprised Muscovites. Natalie notices her phone does not work. They look up in the sky and see an Aurora followed by lights that appear to be falling from the sky. The objects multiply and fall all over the city. One of the lights lands in a clearing with people surrounding it curiously. A Moscow policeman approaches it with his nightstick and is suddenly vaporized. His partner takes out his pistol and shoots at the object, but the bullet is shown to shatter on an invisible force field. The crowd panics as more of the alien creatures appear and vaporize people. A group moves back into the club and shuts the doors closed. The windows of the club shatter and the aliens are able to see people in the club and attack them at will. Someone throws a Molotov cocktail at an alien and the fire keeps it at bay momentarily. The alien then uses electric bolts like arms to grab people and kill them. Ben, Sean, Natalie, Anna and Skyler exit the club through a hole in the wall and find a storeroom to hide out as people are getting vaporized.
The group is running low on food, and it has been 27 hours since they have heard any noises from outside. They all agree they need to leave, and Ben suggests that they might find help at the US embassy. As they exit the storeroom they see the bar is empty; they grab some liquor bottles and look at a map of Moscow they got at a restaurant. Outside the bar, the whole city is empty; there are weapons and many cars sitting outside but no people.
They walk along the streets and hear some noises; they find a Russian lady in her apartment sealing up her window. They ask her for directions, but she tells them in Russian that the ghosts are out there, and they will all die. She does not offer any help and just wants to be left alone. They find a bridge that leads to the Embassy but, it has been damaged by a Russian warship that crashed into it. They try to find another way to cross as they find themselves in Red Square. There is an abandoned police car and a dog barking. Ben and Sean go to the police car and find flares and a map book of Moscow even though it is in Russian. The dog is barking at something they can not see, and they are surprised to see the dog vaporized by an unseen alien. Ben and Sean hide underneath the police car as the alien searches for more victims to attack. The cars siren and lights activate as the alien approaches. The alien can not see them under the car, and they surmise the creatures have weaknesses they can exploit. After it leaves they move into a nearby building and meet up with the girls and Skyler. Inside the building, they find a crashed airliner, and they begin to wonder if they can even survive. Skyler tells them that it is a terrible idea to head to the US embassy, but Sean and Ben feel they need to move on to survive. They surmise that the aliens must use some sort of electrical field for protection and that it seems to activate electrical devices. They find some light bulbs to use as warning devices.
Skyler mentions they need to make smart choices and that you do not know who you are till you find yourself in a troubling moment. Ben suggests they need better clothes; Sean then makes a comment about a coat and tie being the clothes for the end of the world.
Natalie searches for something to wear and undresses. The guys see Natal stripping in the distance, but are interrupted when the light bulbs begin to light up. Natalie hides as an alien searches the store for them. Sean finds Natalie, and they see an alien come close to them, but it does not see them. He suspects that the glass may have blocked its sensors since glass is an electrical insulator. They flee the building and head for the US embassy. Skyler finds an assault rifle and tries to fire it, but he almost loses control of it. He remains where he is and the other move on to the US Embassy.
They find the US Embassy, but it is empty; Natalie finds reports that give them information on the events so far. Most capital cities have been invaded, and no form of resistance seems to work against the aliens. The report does state that underground installations did survive the attack; so the aliens have some weaknesses in their attack plan. They find a map on the table with numbers, and these are estimates of survivors. Natalie reads further that an emergency action station has been setup on a radio frequency but the report ends there. They also find a radio under a birdcage but do not know why it is in there. Sean turns it on, but Anne says it might draw the aliens. Natalie checks her cell phone but, it still does not work. They look outside and see the aliens have them surrounded and are busy digging. They hear gunshots, and find that Skyler has fled. Sean and Ben chase him as they need his ability to speak Russian to understand the radio message. They all hide behind stalled cars, and they tell Skyler he needs to come back. Skyler sees an alien and shoots it, but he is vaporized by the alien.
Sean and Ben go back inside to join the girls, and Sean notices a lit room in a building off in the distance. They suspect that this is what made Skyler leave. They go outside and move carefully in the night not drawing the attention of the Aliens. They are able to make it to the building as sunrise comes. Inside the building, they encounter a young lady with a gun who speaks to them in Russian. They answer in English and are happy that the lady named Vika (Veronika Ozerova) does answer back in English. She tells them to follow her, and she takes them in a room surrounded by a metal cage. They meet an older Russian man named Sergei who is happy to see more survivors. He locks the cage behind him and explains that the light is there to draw people to him; he was able to bring Vika and now them. Vika explains that they are in a Faraday Cage and the aliens can not see inside it.
They hear a radio broadcast in Russian and Vika translates it for them; the K152 nuclear submarine is in the Moscow River, and will pick up any survivors that reach it before the next morning. They also reported that a number of other submarines are doing the same around the world; Sergei comments that the submarine are the perfect Faraday cage. Vika tells the ladies she will need their help getting supplies for their journey. Sergei shows Sean and Ben a microwave gun he built that he believes can be used to disrupt the electrical shield of the aliens. While getting supplies the aliens spot the 3 ladies in the building and move in to attack. Vika sees them and tells Anne and Natalie to run back to Sergei’s apartment. They run inside but can not lock the cage; they try to block the doors, but an alien follows them in and spots them all. Sergei takes the rifle and fires it at the alien; it appears to work, and disrupts the alien, but the creature is still able to attack; killing Sergei. The rest of the group flees the building as Natalie sets some fuel on fire, but Anne does not make it and is vaporized.
The group moves on trying to reach the river, but they encounter a group of armed men dressed in metal and carrying makeshift shields. They are able to attack an alien with gun fire, a flamethrower and an RPG. These weapons combined are able to kill the alien; they all celebrate their kill. They are led by a man on horseback who explains that the aliens are weakest when they use their lightening. Sean picks up a piece of the dead alien; it appears to be hard and glasslike. The militia is friendly and more than happy to offer help and protection; they share what they know about the aliens and information about the submarines. The leader of the group is skeptical and tells them that the river is too far, and there are too many aliens in their way.
Sean says they will go, and is joined by Natalie as this is not her home, and wants a chance to go home. Vika says she will join him along with Ben and Natalie. The Russian militia leader accepts their decision; recommending that using the subway tunnels might be the best way to reach their destination. They move within the subway tunnels but now they are being tracked; they throw light bulbs and find they are lighting up. The aliens attack, and they flee; Ben gets grabbed by one of the creature electrical arms and is killed. They are able to reach the river and find a boat to hide inside. Sean is upset at losing his best friend, and Natalie comforts him as Ben had done for her earlier when she lost Anne. He tells Natalie about how he and Ben became friends when they were little. The militia members are able to the get the boat to drift down the river with the current in the hope that they can find the submarine.
The boat runs into an obstacle, and they are all forced on deck to try and figure if they can free it. They all witness a number of alien ships using their beams to lift up metals and resources. The Russian surmises that they are strip mining the planet for metals that they can use. Vika sees the submarine nearby and states they will make it; suddenly a building off in the distance is destroyed by the aliens; the debris crashes into the boat and all are forced into the river. Sean and most of the others are able to swim out to the Submarine; the Captain welcomes them but tells Sean they will need to leave soon. Sean tells him that Natalie is lost, and he knows she is still alive when they see a flare launch in the distance. The Captain agrees to wait; the technicians on the submarine look over the microwave gun and they offer to build more with better batteries. Sean and the militia leader go out with a group to search for Natalie.
They throw out cell phones as warning devices, and proceed to a group of buses that Sean thinks Natalie may be hiding inside. Sean is confronted by an alien, and his weapon does not work; he is saved by his group who are able to kill the alien after he finally gets it to work. They setup an ambush zone with Vika spilling water from tank truck to help amplify the effect of the microwave guns. Natalie is hiding inside a bus, but there are too many aliens surrounding outside. Sean checks each of the buses but can not find Natalie.
The militia group lures three aliens over the gas pool that Vika then lights; they are all able to see the aliens and open fire killing all three trapped aliens. Sean and Nat meet but their bus starts moving as an alien enters the bus and uses an electrical arm to grab Natalie. Sean uses the microwave gun to stun the alien, but the batteries are drained. The alien moves closer to Natalie forcing Sean to throw the piece of a dead alien he picked up earlier at it; it causes the alien to die.
They make it back to the submarine, and Sean asks the militia if they will join them; he tells them that this is their home, and they need to stay and fight. It is up to Sean to let the rest of the world know what they have learned about the aliens. The submarine leaves and sets sail for the open ocean.
A Russian technician repairs Natalie's cell phone; she is able to get a text message from her mom. It states she is safe and that she loves her and hopes to see her soon.
Sean and Natalie almost kiss, but are noticed by Vika who is listening to music on her cell phone. Later they look at a map with the captain listening to shortwave radio reports coming in about groups who are fighting back against the alien invasion. One group in Paris has even brought down one of the mining towers. Sean says this is how it starts.
The submarine sails on as the movie ends.
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