A lobster pot illustrates the danger of intimacy in Todd Field’s restrained but flawed adaptation of an André Dubus story. If two lobsters climb in, laconic Maine native Dr. Matt Fowler (Tom Wilkinson) explains, all is well, but if three are "in the bedroom . . . " That third in his bedroom might be his son and only child, Frank (Nick Stahl), whose best interests represent a sore spot between Matt and wife Ruth (Sissy Spacek). At issue is Frank’s fling with Natalie (Marisa Tomei), an older, soon-to-be divorcée with two kids and an ex who’s a flaming asshole. Ruth sees nothing but trouble for her Ivy League–bound pet; Matt sees, maybe, vicarious youth. We all see the brutal crime coming, and for the most part Field sets the melodrama in such an authentically detailed setting (at times it seems to slip into Frederick Wiseman’s Belfast, Maine) and with such convincing acting (too much so with Spacek, who comes off as a shrew) that they almost overcome the generic gratifications at the end.