Jauntier than any of Kelly Reichardt’s previous work, “The Mastermind” packs an ironic punch. That the title need not be taken literally becomes clear right from the start, of course; that the film’s shaggy-dog tone belies something far-sadder and more allegorical takes a bit longer to set-in.

Josh O'Connor plays a family man whose under-planned theft from a local art museum goes amusingly awry in Kelly Reichardt's inspired "The Mastermind"

Few minds could be less masterly, you might think, than the stoner sponge between the ears of J.B. (Josh O’Connor), who, in Kelly Reichardt’s Cannes-closer The Mastermind, conceives a plan to steal four paintings from the art gallery that is the chief weekend haunt for his family.