High school student Sakuya Outsuki works as a detective, a profession he inherited from his famous father, Tatsuya Outsuki. Both father and son possess a strange and useful gift for the job: functional immortality. Whenever Sakuya is killed, he returns to life. However, this power comes with a steep price, as he retains all the trauma and pain from each death. Unlike his thrill-seeking father, Sakuya prefers to avoid danger and stick to low-risk cases like investigating cheating spouses or finding lost pets.

Assisting him is Lilithea, a beautiful and highly capable sixteen-year-old girl with silver hair who serves as his partner. While observant and skilled at her job, she has a quirky, jealous, and sometimes needlessly mean personality, often distracting herself with games like darts.

The story primarily unfolds in contemporary Japan, beginning at the Outsuki Detective Agency. The first major arc places Sakuya and Lilithea on a luxury cruise liner. What is supposed to be a simple job following a film director for an adultery investigation quickly spirals into a deadly affair when the duo finds themselves entangled in the murder of a wealthy scion from a manufacturing family. As Sakuya is inevitably killed during the case, he and Lilithea must use his ability and her deductive skills to solve the mystery before dying again. The solution involves a classic fair-play clue based on English letters or katakana characters.

This arc is bookended by the looming presence of Sakuya’s father, who is off working as a specialist on a high-stakes airplane hijacking. The second and final volume of the manga shifts focus after the elder Outsuki goes missing. With the legendary detective gone and the agency’s other sleuths having left, Sakuya and Lilithea must work together to protect his legacy, solve the mystery of his disappearance, and find a home they can return to.