Tantei Jinguuji Saburou: Fukushuu no Rondo

The 25th anniversary title of the saga.

The story starts with Jinguuji waking up, only to find himself bound and being used as a punching bag by some gangsters. They seem to want information about a certain something from Jinguuji (and they also seem to have a personal grudge against him), though he honestly has no idea what they're talking about. Jinguuji manages to escape, only to discover that the police found the dead body of an ex-client of him in the trunk of his car, making him the prime suspect in the murder case. Chased by both the gangsters and the police now, the Shinjuku detective has to clear his name and find out what happened.

[from Boku no Jikenbo]