An assassin (Brad Pitt) is given the name Ladybug in an effort to put his streak of bad luck to rest. With the help of his handler, Maria (Sandra Bullock), he's given a relatively easy assignment with a low chance of casualties in order to build his confidence: retrieve a briefcase on a bullet train departing from Tokyo. He takes an assortment of gadgets to help him with his job, but leaves behind the gun he's been offered, because he now has a therapist who's helping him to become enlightened, and guns don't mesh with that way of thinking.

The mission starts out promising, but quickly goes wrong when it becomes clear the train is filled with an assortment of other assassins, some of whom reappear from Ladybug's haunted past. Not realizing their individual assignments are all somehow connected, the highly trained criminals take part in a deadly game of survival on one of the fastest modes of transport in the world.

Adapted from Kôtarô Isaka's Japanese novel of the same name.