American Ultra is a fast-paced action comedy about Mike, a seemingly hapless and unmotivated stoner whose small-town life with his live-in girlfriend, Phoebe, is suddenly turned upside down. Unbeknownst to him, Mike is actually a highly trained, lethal sleeper agent. In the blink of an eye, as his secret past comes back to haunt him, Mike is thrust into the middle of a deadly government operation and is forced to summon his inner action-hero in order to survive.

Three high school seniors throw a party to make a name for themselves. As the night progresses, things spiral out of control as word of the party spreads.