Double Jeopardy

When Joseph Carrington kills a man for whose alleged murder he has just spent twenty years in prison, DCI Forsyth and DS MacRae are keen to find out who told him of the victim's new identity. There are a number of suspects, but Carrington refuses to point the finger at any of them. When Carrington and a crony of his, Keith Edwards, are murdered, MacRae is astounded to find that Forsyth is prepared to take a case to the Procurator Fiscal because of what Edwards had to eat just before he died. But Forsyth is not fooling and the team are amazed by the brilliance of the solution that Forsyth has arrived at by the use of logical deduction.