The Boyfriend by Thomas Perry

Not great Perry but still very enjoyable. Excellent narration by Robertson Dean. PW: Jack Till, who has retired from the LAPD after a respected career as a homicide detective, now works as a private investigator, comfortable chasing down routine cases while visiting his 24-year-old daughter, Holly, who has Down Syndrome. But when the parents of a recently murdered young girl, about Holly's age, ask for his help when the police come up empty, Till reluctantly takes the case.