This is a movie where a disavowed spy fires up a chainsaw on an airplane in flight. Get on board, or be bored elsewhere.

Hartnett and Chandran’s laid back chemistry steady the film’s turbulent tonal shifts, adding a punch that the shakily choreographed action lacks.

Surprisingly, Hartnett’s Lucas hasn’t worn out his welcome, even if the movie around him has fallen apart midair. Ergo, the old truism has never been truer: When it comes to “Fight or Flight,” your mileage may vary.

Fight or Flight should be a lot more fun than it is.