Two sci-fi geeks take a pilgrimage to America's UFO heartland. While there, they accidentally meet an alien who brings them on an insane road trip that alters their universe forever. For the past 60 years, an alien named Paul (voiced by Seth Rogen) has been hanging out at a top-secret military base. When he discovers he's been taken prisoner, the space-traveling smart ass decides to escape the compound and hop on the first vehicle out of town - a rented RV containing Earthlings Graeme Willy (Simon Pegg) and Clive Gollings (Nick Frost). Chased by federal agents and the fanatical father of a young woman that they accidentally kidnap, Graeme and Clive hatch a fumbling escape plan to return Paul to his mother ship. And as two nerds struggle to help, one little green man might just take his fellow outcasts from misfits to intergalactic heroes.