They say pot makes you paranoid. In Mike Howell’s case, apparently not enough.

Mike (Jesse Eisenberg, sporting his worst hairdo ever) is your average small-town doobie-rolling slacker whose only ambitions are to draw monkey comics and marry Phoebe (Kristen Stewart), his true love and partner in weed. That is, until he finds out he’s the takedown target of highly trained government assassins, that he used to be one of them and that he can waste a dude with a spoon.

Mike’s assets are deemed no longer necessary by CIA boss Adrian Yates (an improbably sinister Topher Grace), who gives orders to terminate him.

Sympathetic fellow agent Victoria Lasseter (Connie Britton) charges up Mike’s dormant powers and tries to warn him while he’s pulling down a night shift at the dollar store. But it’s not until he has dispatched a couple of guys sent to kill him that he starts to realize something is awfully amiss and he’d better channel his rusty skill set, fast.

In addition to Grace and Britton, the supporting cast is a who’s who of known TV and film names. Walton Goggins, John Leguizamo, Tony Hale, Lavell Crawford and Bill Pullman all pop up, romping their way through supporting roles with relish (except for Pullman, who’s been a sullen screen presence since “Independence Day”).

But the brightest star of this picture is screenwriter Max Landis, who pulls off a masterful mashup of action, comedy and romance, with bits of animation tossed in. In lesser hands, fledgling director Nima Nourizadeh could have ended up with a real mess. But together the two manage to bend genres into something that feels new, even if a few too many action scenes in a row flatten out the middle.

It might seem impossible to squeeze tender loving moments between all the sarcasm and surreal mayhem. But the romance part works, largely because of the easy intimacy between Eisenberg and Stewart, reunited after their first pairing in 2009’s “Adventureland.” Her laid-back, laissez-faire demeanor is a perfect foil for his nervous, nerdy energy.