A potentially interesting idea jumps the rails halfway through the father-son drama “I Know You Know,” the second feature by Welsh-born writer-helmer Justin Kerrigan (“Human Traffic,” 1999). Aside from its vivid, ’60s-style main title (which seems incongruous for a movie set in the late ’80s), there’s little to flag this as the work of the same filmmaker, as it fails to develop the partly wacky, partly serious idea with any consistent tone. Small-scale item, which hangs on a twist an hour in, looks headed for the tube at best.
Robert Carlyle plays doting father Charlie, who appears to work as a spy and has to lie low for a while. Settling incognito into the southern Welsh town where he grew up, Charlie puts his 11-year-old son, Jamie (Arron Fuller), into school and sets about doing a job he promises will set them up for life. Bolted onto the increasingly silly plot is a routine coming-of-age story in which father and son try to understand each other as Charlie’s paranoia increasingly pulls them apart. Carlyle plays mostly manic, though Fuller is fine. Tech package, blown up from 16mm, is modest.