There’s something about Kate Frazier (Kelly Macdonald) that attracts the crazies. After the adorable Scottish lass flees her abusive cop husband (Bobby Cannavale) for an unidentified American city, she soon stumbles into trouble when she prevents the suicide of stone-faced assassin Frank Logan (Michael Keaton, who also makes his directorial debut here). Enter another borderline personality in the doughy form of Dave Murcheson (Tom Bastounes), the alcoholic, chain-smoking detective investigating a string of murders committed by Frank. Despite Kate’s Zen-like calm (because of?), all of these live wires–made more so by their jones for her–cross and, yeah, spark over the course of this subtle and engaging black comedy/thriller. Assorted other loons hover on the margins of Kate’s fractured life, and it’s to the actors’ and screenwriter Ron Lazzeretti’s credit that none of the characters, no matter how minor or major or deranged, fall into caricature. The no-holds-barred humor helps, as does the clinical distance of Keaton’s direction. He employs a detached style that mirrors the characters’ isolation from reality–and themselves. The only quibble, and it’s kind of a biggie, comes at the end, when we realize that the driving force of the narrative is to remain a mystery. Such calculated ambiguity has no place in a film so otherwise concerned with probing the finer points. (Rated R, 110 minutes)The Merry Gentlemen Harvard Exit, 3:45 p.m., Sat., May 30.