Catherine (Julianne Moore), a doctor and David (Liam Neeson), a professor, seem from the outside to have a perfect life. They have a seemingly happy marriage and have a teenage son who adds to the perfection of their life. Catherine, however, is harboring fears and suspicions about her husband's fidelity, which are sparked by David missing a surprise party Catherine was throwing for him. With this final straw, Catherine decides to hire escort Chloe (Amanda Seyfried) to seduce David, to discover once and for all his loyalty to his wife. Catherine gets increasingly involved in the game, directing Chloe's actions and requiring her to report back everything that happens between Chloe and David. Will Catherine's test reveal the results she expects, or will Catherine find herself in far too deep with a difficult problem?