Sighs of awe follow Eun Chaerin wherever she goes, as expected for the perfect protagonist of a run-of-the-mill romance novel. She was once the novel's reader in the real world, and now she has the opportunity to live it herself and have her storybook ending with the male lead, Yu Jeha. But everything goes south on the day Jeha is supposed to confess his feelings, for he turns into a disfigured zombie and bites Chaerin.

Instead of dying, Chaerin is forced to relive the same day, trapped in the loop of a bizarre zombie outbreak, unable to save Jeha. She desperately clings to him, as he is the only person she can see—all the background characters appear as nothing more than dark silhouettes to her. After almost four hundred repetitions, something unprecedented happens: a formless classmate pulls Chaerin to safety, and she catches a glimpse of their true appearance before dying again.

The possibility of unlocking and revealing the extra characters fills Chaerin with new vigor. If she forgets about saving Jeha and focuses on finding this unknown extra in her next regression, she may be able to reach her happy ending after all.