When her inability to commit leads to a breakup with her girlfriend (Julianne Nicholson), opera-loving writer Allegra (Elizabeth Reaser) winds up in the bed of amiable professor Philip (Gretchen Mol). He is so smitten with Allegra that he dumps his lover, Grace (Justin Kirk), and convinces Allegra to continue their affair. When Allegra meets Grace, sparks fly, and she begins a parallel romance, unaware that her new lover is the woman Philip left to be with her.