Three Summers opens, a young man with a difficult past leaves his present home in the city of Hong Kong and hearkens back to the fishing village of his youth. Against the backdrop of that locale, his young sister has recently befriended a group of adolescents who visit the isle perennially - every summer - and who share their individual stories with her. One tale at a time, she begins to experience life vicariously through the others' recollections.

Hong Kong Triad enforcers raped a young woman and left her for dead. But Sally survived and, thanks to a chance encounter with a firearms instructor, she transformed from a defenceless girl into a deadly assassin—a fearsome executioner. With a gun in her hand and under the guise of a flirtatious beauty, she declares war on the Triad.