Derailed belongs to the long movie tradition in which a basically good man makes a moral misstep that leads to his complete undoing, yet I can’t think of another movie morality play that details the undoing to such a ludicrous degree. A dependable if distracted husband and father (Clive Owen) begins an affair with a stranger on his commuter train (Jennifer Aniston, struggling to stretch). When the hypocritical hammer comes down (it’s always amusing to see how such movies awkwardly segue from frisky titillation to tsk-tsk moralizing), it lands with a particularly vicious, highly implausible thwack.