The Root of All Evil — Gavin MacDonald

With DCI Forsyth on holiday, his squad investigates the murder of a couple in what looks like a gangland killing, and it turns out that the couple have lied as to how they obtained their wealth. When DS MacRae hears of a previous, similar killing, the squad is able to make the connection between the two incidents and trace other people involved, who may also be at risk. But none of the others is prepared to cooperate and, when two of them are murdered in St Andrews, MacRae joins an Inspector from the Fife Constabulary in trying to find who is behind the murders, but without success. When Forsyth comes back early from holiday, he takes over the investigation and, by the use of logical deduction, arrives at the identity of the murderer.