It’s one of the most common story premises in film noir: a cop goes undercover to infiltrate a crime ring. What rarely happens, however, is that the cop feels a sense of belonging with the criminals and decides to switch sides. That’s essentially what happens in Cliff Owen’s Offbeat (US: The Devil Inside), a compact but well-done British noir in which the cop not only befriends the criminals but ends up falling in love with one of them. The cop in question is a former MI5 “lone wolf” named Layton (William Sylvester) who’s recruited by Scotland Yard to play a counterfeiter named Steve Ross; the always underrated Sylvester is excellent as the scowling, laconic misanthrope who comes alive when he joins the gang, and especially after meeting “moll” Ruth Lombard (Mai Zetterling) with whom he starts a romance almost immediately. The gang, led by James Dawson (Anthony Dawson) and Johnny Hemick (John Meillon), plans and executes an elaborate robbery of a jewelry store which involves an impressive feat of tunneling in from the sidewalk; dividing up the loot, however, will bring a new set of obstacles. It’s an entertaining film that will keep viewers glued for the 71-minute runtime even if Ken Jones’ peppy jazz score seems ill-suited for the subject matter at times.