The alien race known as the Boov are very good at one thing – running away. On the run from their enemy, the Gorg, the Boov have found a new planet to call home – Earth. Led by Captain Smek (voice of Steve Martin), they commence their friendly invasion of the planet, relocating the humans to other parts of the planet while the Boov inhabit their homes.
One of the Boov, Oh (voice of Jim Parsons), is a more excited, free-thinking member of the species. He invites all the other Boov to his apartment for a housewarming party. None of the Boov show up, and Oh is left feeling lonely.
Not far from Oh is a teenage girl named Tip (voice of Rihanna). Her mother Lucy (voice of Jennifer Lopez) was separated from her during the invasion, leaving Tip with her pet cat Pig and fueling her hatred for the Boov. One Boov enters Tip’s home, leaving her no choice but to make a run for it. She takes her car and decides to take it upon herself to find her mother.
Oh runs into the street to find a Boov cop named Kyle (voice of Matt L. Jones), who, like the rest of the Boov, are annoyed with Oh. He invites him to the party, and then decides to send a mass invite to every Boov on Earth. Oh hits “reply all”, which goes to EVERYBODY in the galaxy, including the Gorg. The Boov panic and declare Oh a fugitive. The little alien just barely manages to escape. He runs into a convenience store to grab stuff, just as Tip and Pig are doing. Tip runs into Oh and shoves him into the fridge, trapping him with a broom. She decides to leave him there, until her car fails to start. Oh offers to fix it, so Tip reluctantly lets him out. He turns it into a hovercar that runs on slushies. Oh hitches a ride with Tip when he promises to help her find her mother, but they have to go to Paris to find the Boov Command Center and locate her through that.
Smek summons the smartest Boov to come up with a solution to stop Oh’s invitation from reaching the Gorg in less than 30 hours. After a few bad suggestions, one of the smart Boov starts to say they can delete the invitation, until Smek takes credit for that plan. The Boov are shocked to find that they can’t log into Oh’s email because his password is unique, unlike everyone else’s (it’s “password”). Smek sends Kyle to find Oh and arrest him.
Tip and Oh stop at a gas station. Oh tries to reroute the GPS on the car to take him to Antarctica to get away from every Boov in sight. Kyle shows up and tries to arrest Oh, when Tip comes back and knocks some boxes over him. She shoves Oh around when she realizes he tried to ditch her and back out on his promise. She straps him to the passenger’s seat and flies the car herself, evading Kyle and making it over the ocean.
During the ride, Tip introduces Oh to her favorite music. He begins to feel an involuntary sense to dance. This gets so intense for him that he has to jump into the ocean to cool his core. Tip waits worriedly for hours until Oh reemerges. She chastises him to scaring her. Oh learns that Tip already feels lonely like him without her mom. The two decide to work together and they open up to each other on the rest of the trip.
They make it to Paris and locate the Boov Command Center, which is in the now-floating Eiffel Tower. While the smart Boov continue to try and find a way to break into Oh’s password, Oh gets in himself and deletes the message seconds before it reaches the Gorg. He then plugs in Tip’s brain to help him get an idea of where to find Lucy. They trace her location to Australia, where she is actively looking for her daughter. Tip hugs Oh for this. The other Boov then find the two and try to “erase” Oh. Tip messes with the gravity manipulation system and causes the whole Tower base to tilt upside down. She and Oh find the car and head for Australia.
When the two wake up, they see other Boov riding by them in fear. A Gorg ship is close behind them. Tip and Oh manage to knock it down, but in the process lose their slushie fuel. Oh figures he can repair the car with some Gorg technology from the fallen Gorg ship. They come across it and see that it’s actually a drone. Oh recovers a special chip and uses it to get the car up and running.
Tip and Oh make it to Australia and see the Boov evacuating to their mothership. When they land the car, Tip starts to run for her mother, but Oh tries pulling her toward the mothership for safety. Oh claims that Lucy is on the ship, but Tip knows he’s lying. She gets angry at him for trying to break the promise again, and she declares that they were never friends. Heartbroken, Oh returns to the ship. The Gorg come close to the Boov ship as they flee in terror. Oh pulls out the Gorg chip and uses it to fly the ship further away from the Gorg. The Boov become astonished at Oh’s plan. Smek becomes upset and reminds everyone that he’s the captain. Oh defies him and says he’s a bad one since everything he told them about humans was a lie. Smek orders he be erased, until Kyle steps in and defends Oh. He grabs Smek’s “shusher” (a scepter thing with a rock on it) and gives it to Oh, stating that he should be the new captain. Although uncertain at first, Oh knows what he has to do first.
Tip goes everywhere she can to find Lucy, but nobody can help her. Defeated, she sits in a corner and cries. Oh returns to her side and helps her track down Lucy. The mother and daughter finally reunite and thank Oh. The Gorg mothership then descends upon the planet. Oh realizes that they want the rock on the shusher, since Smek stole it from them before. Oh runs to the ship to try and get it’s attention, locking Tip and Lucy in the car to avoid them getting in trouble. Tip breaks out of the car and shines a light in the Gorg’s face to bring his attention to Oh as he holds the rock up. The Gorg halts the ship as it mows down the ground, with Oh in its path. Tip rushes to rescue him, but it appears that Oh gets crushed beneath the machine. It starts to pull back, and Oh is unharmed. Tip and Lucy run to Oh and hug him. The Gorg emerges from the ship, and Oh returns him the rock. The Gorg emerges from its armor to show that it’s a harmless starfish-type creature. Inside the rock are the next generation of Gorg, as this Gorg is the last of his kind. He thanks Oh and departs. Oh becomes a hero to both humans and Boov.
Oh finally gets to have his party at his apartment, with humans and Boov in attendance. Tip plays her music and gets the rest of the Boov to experience dancing for the first time. We then see that other Boov, including Smek, are partying on the moon, while other ships from other planets head to Earth for Oh’s party.