As expected for the ideal protagonist of a standard romance novel, Eun Chaerin is followed by sighs of awe wherever she goes. She was once the novel's reader in the real world, and now she has the chance to live it out herself and secure her storybook ending with the male lead, Yu Jeha. However, everything goes wrong on the day Jeha is supposed to confess his feelings, as he transforms into a disfigured zombie and bites Chaerin. Instead of dying, Chaerin is forced to relive the same day, trapped in a loop of a bizarre zombie outbreak, unable to save Jeha. She desperately clings to him, since he is the only person she can see—all the background characters appear to her as nothing more than dark silhouettes. After nearly four hundred repetitions, something unprecedented occurs: 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.