"Somebody I Used to Know" follows workaholic Ally (Alison Brie) who, on a trip to her hometown, spends a night reminiscing with her ex-boyfriend Sean (Jay Ellis), which makes her start to question everything about the choices she's made and the person she's become. Things only get more confusing when she meets Cassidy (Kiersey Clemons), a younger woman who reminds her of the person she used to be.