Bloody and Invisible Hand — Gavin MacDonald

While DCI Ian Forsyth is on holiday, DS Alistair MacRae has to lead the squad in an investigation of the murders of three ex-Army personnel from a unit that operated in Northern Ireland during the Troubles. The first murder takes place during a reunion in a student residence in Edinburgh, the second in the ex-captain's house near the city and the third on a common close by. The second and third murders appear to have been committed by an invisible killer. MacRae believes that he can explain the first two murders but is completely baffled by the third. It falls to Forsyth, on his return from holiday, to arrive at a solution to all three murders by the use of logical deduction and to provide tangible evidence that his solution is the correct one.