Masaki Aiba identifies himself as "Kizoku" ("Aristocrat") and works as a private detective for a hobby. Nobody knows his age, address or anything about his family. The actual deductions and investigations are carried out by his employees including his butler, maid and chauffeur. He only has a good time talking to the women involved in the cases.

Meanwhile, Aika Takatoku works as a private detective. She competes with the Aristocrat Detective to solve cases.

Kizoku Tantei is an adaptation of Maya Yutaka's 2010 novel of the same title.