"Everybody's got a crazy ex -- hell, I'm somebody's crazy ex." That quote, spoken by Ali (Whitney Cummings) to her best friend Julia (Rosario Dawson), represents a truism that Julia will soon learn firsthand. She has just left behind her successful career as a publication editor in San Francisco to join David (Geoff Stults), her future husband, in a small town on the other side of California. His ex-wife Tessa (Katherine Heigl) and their daughter Lily (Isabella Kai Rice) are still very much in the picture, as David and Tessa split time with Lily and are seemingly on good terms.
However, Tessa takes the role of jealous ex-lover to the next level when she begins to interfere in the soon-to-be-married couple's relationship. Unable to witness the happiness that she believes should still be hers, Tessa hatches a plot involving a certain someone from her new rival's past: Julia's restraining order on an ex-boyfriend named Michael (Simon Kassianides) has just expired, and the memories of their abusive relationship relentlessly haunt her during the transition to her new life. Tessa tries to use Michael to terrorize Julia, but when this scheme doesn't go as planned, she's forced to take matters into her own hands in an attempt to steal back what is "rightfully" hers.
While this labyrinthine drama successfully keeps the viewer wondering what will happen next, it does little to hide a shallow and underdeveloped plot. It's almost unbelievable just how far Tessa will go to get her way, as she proceeds with painstaking deliberation until the most important part of her plan. This inconsistency is further emphasized by David's naïve ignorance of her obvious insanity, and it's almost too late before he realizes that Julia's suspicions were correct all along. The film's conclusion is telegraphed far in advance, as a battle between David's future and past wives ends in a display of melodramatic vanity. In a story where plot holes are as commonplace as murderous ex-lovers, the only thing you can count on in Unforgettable is that the main characters will stay true to their one defining personality trait.