Scott Pilgrim, a directionless 22-year-old bass guitarist for the band "Sex Bob-Omb," becomes infatuated with a mysterious American girl, Ramona Flowers, after seeing her in a dream. Despite dating a high schooler, Knives Chau, Scott pursues Ramona, only to discover that he must defeat her seven evil exes in combat to date her. These exes are members of the "League of Evil Exes," each with unique powers and motivations. As Scott battles each ex, he juggles his relationship with Knives, his band's shot at success, and his growing feelings for Ramona, discovering that his quest is about more than just winning her heart—it's also about self-discovery and facing the consequences of his own past relationships.

The battles with the exes become increasingly challenging, testing Scott's resolve, skills, and stamina. Each fight is intertwined with the Toronto indie music scene and Scott's everyday life, blending video game-like action with the complexities of real-world relationships. As Scott progresses, his interactions with friends, bandmates, and the exes reveal the diverse social dynamics he's entangled in. Throughout the confrontations, Scott learns more about Ramona's past and the baggage that comes with it. Meanwhile, his rivalry with the exes starts impacting his relationships, leading him to question the nature of love, the price of happiness, and what he truly wants from his life.