"A Good Marriage" features a gripping zinger of a plot hook at the end of its first act, then spends the next hour-plus radically dissolving before the viewer's eyes. Joan Allen (2012's "The Bourne Legacy") is the film's one superlative constant as Darcy Anderson, a woman whose picture-perfect life is ineradicably shattered when she makes a horrifying discovery about her husband of twenty-five years, Bob (Anthony LaPaglia), while he is away on a business trip. This is a smashing setup, and Allen brings a kaleidoscope of emotions to Darcy as she struggles with how to react and what to do with the knowledge that Bob isn't at all who she thought he was. The moment her spouse shows back up, however, the film—directed by Peter Askin and written by Stephen King, adapted from a novella in his 2010 story collection "Full Dark, No Stars"—short-circuits with a series of story turns so implausible it becomes a waiting game for Darcy to wake up. She never does because it is, sadly, supposed to be reality.

In the face of wild contrivances and inconsistent character actions, Joan Allen does her best to hold the threadbare material together. The quandary Darcy faces is involving, but it also increasingly infuriates as she turns her back on one opportunity after the next to do the right thing. As the manipulative, sociopathic Bob, Anthony LaPaglia (2010's "Legend of the Guardians: The Owls of Ga'Hoole") also must act outside the realm of believability, cheerily going about his days while ignorantly assuming his marriage is untarnished and still going strong. When the twist—if one can call it that—arrives at the end, it comes with an "is-that-all-there-is?" shrug. Meanwhile, a subplot involving a private investigator (Stephen Lang) goes nowhere special, only serving to bloat the running time. A Lifetime melodrama posing as a big-screen thriller, "A Good Marriage" starts with the germ of a provocative premise, then proceeds to take it in a direction that betrays the audience's intelligence.