Lee Blessing’s engrossing character study-cum-murder mystery chronicles the 60-year relationship of two small-town gay men, which is fatefully changed by an incident of horrifying violence. Jumping back and forth in time, the drama requires three pairs of actors to play the central characters at different ages–as teenagers in 1948, middle-aged guys in 1973, and old men today. Blessing’s unusual narrative structure demands performances of unrelenting honesty, and director Jarrett Dapier’s wonderful cast rises to the challenge. Even in its most intense moments of intimacy or brutality, Thief River is devoid of sentimentality, melodrama, or political grandstanding as it asks us to consider how its characters’ lives–and by extension our own–are shaped by the conflicting values of changing times. a Through 3/25: Thu-Sat 7:30 PM, Sun 2 PM, Side Project Theatre, 1439 W. Jarvis, 773-973-2150, $15-$20, two for one Thu.