The London Tram Murders

Detective Inspectors Vance and Shepherd reunite in the second book in John Broughton's Vance And Shepherd Mysteries. After a murder is committed in a quiet suburban subway under a tramline, it becomes obvious that the murder squad is dealing with a copycat killer.
The murder is an uncanny repeat of their previous case, and their inquiries are complicated by the presence of the main suspect's doppelganger, Melanie Bradshaw. The brilliant chemistry master student has solid alibis but Shepherd, flying in the face of the contrary evidence, is convinced that the deceased serial killer's sister and Melanie are the same person.
As the killings continue, Vance and Shepherd face increasing pressure from above building. Can they apprehend and bring the killer to justice before more lives are lost?