그 해 여름 내 심장이 멈췄다.

High school senior, Isabel, will soon die from a serious heart condition. She has a secret crush on her best friend Alex, and plans to confess her feelings to him after graduation. However, a huge misunderstanding in the middle of senior year ruins their friendship. Alex now holds a grudge against Isabel. He even lets her classmates bully her. Ten years later, Alex finds a collection of short vlogs that Isabel left for him. The videos reveal a shocking truth, a truth that completely changes Alex's world.