Homicide detective Ding Qi (Bai Jing Ting) accidentally gains a strange ability: under specific circumstances, he can turn back time to the start of the day up to five times. Ding Qi utilizes his new power to solve difficult cases by traveling back in time to gather evidence, then putting all the pieces together on his fifth loop. However, when Ding Qi receives an ominous warning from a suspect nicknamed "Squid," he starts to wonder if others have also gained the ability to time travel. Ding Qi's investigations lead him to a genetic research group where several executives have recently died, raising even more questions. Alongside researcher An Lan (Janice Man), Ding Qi commits to uncovering the truth behind these deaths – even if it means making the ultimate sacrifice. This drama was adapted from the novel "Ni Shi Zhen Cha Zu" (Time-Reversal Investigation Unit) by Zhang Xiao Mao.