Joe Sangster, a doctor at a local health clinic, hires Greg McDowall after one of his clients, a prostitute, dies from a drug overdose he suspects was administered to her.

Having seen Veitch speaking to a notorious pimp, McDowell is keen to find out just how much Doctor Sangster knows. The firm faces serious financial difficulties.

After the bomb that was meant for him kills Ackroyd instead, McDowell tries to find out what he can, but both the police and Doctor Sangster refuse to tell him anything.

McDowell believes his client's wife was actually murdered by a serial killer.

Katherine Dunbar begins to think McCandlish might be innocent when the police discover that his wife's cause of death is the same as the Street Killer's victims.

Naismith manages to track down his wife, Dunbar's ethics are challenged, and McDowell makes a discovery that puts Sarah's life in jeopardy.