Mara is a young creative writing professor struggling with problems in her marriage to an experimental musician. One day, she runs into Matt, a charismatic, free-spirited author from her past, when he wanders onto her university campus. Bonded by their shared interests, the two gradually become closer. When Mara’s husband unexpectedly cancels plans to drive her to an out-of-town conference, Matt accompanies Mara on the trip instead. Along the way, the tension surrounding their undefined relationship slowly grows.

The Leaving Party follows a group of friends over the course of a summer's day. The film examines the way women maneuver their lives with humor, storytelling, and camaraderie.