The cast has a great good time — Oyelowo, playing a stooge who slowly gets wise over the course of the film, has a chance to loosen up after playing Martin Luther King Jr. in “Selma,” and Copley (“District 9,” “Chappie”) is a most engaging wild card, since you don’t know whether his character will follow his murderous or helpful impulses and neither does he.
We also have a former hired killer (“District 9” star Sharlto Copley) and two inept American drug smugglers (Amanda Seyfried, Harry Treadaway), all of whom cross paths with Harold’s increasingly daft adventures.