Head Games by Thomas B. Cavanagh

With a brain tumor that he has nicknamed "Bob," ex-police detective Mike Garrity is trying to deal with what he feels is a death sentence. A colleague comes along with an lucrative offer to find T.J., the star of the band Boyz Klub, who has gone missing. Mike agrees to take the job believing that the money would be nice to leave to his 15 year old daugther Jennifer when he's gone. He will also score points with Jennifer, whom he rarely sees, because Boyz Klub are her favorite band. Mike works hard to find T.J., but then discovers that other people are also looking for him with a more sinister plan in mind. Head Games is a mystery with humor despite the presence of "Bob". Mike Garrity is an amusing, pessimistic character.