A rescue on a riverbank brings hungry, homeless Atsushi Nakajima into contact with Osamu Dazai, an eccentric supernatural detective with a penchant for suicide. Dazai is investigating a mystical tiger connected to the orphanage that recently expelled the 18-year-old. Strange incidents had troubled the orphanage for weeks, and Atsushi was blamed despite seeming to be the only person unaware of the creature.
With Dazai's partner, Doppo Kunikida, they uncover the truth behind the tiger, but the answer puts Atsushi in a difficult position. Further bizarre events lead to his being pressured into joining their detective firm. Among its enigmatic investigators, he takes on unusual cases that the police cannot handle.
