Private detective Edward Mercer (Richard Todd) is sent to Venice to find war-time Italian partisan Renzo Ucello (John Gregson) and reward him for aiding the escape of a wealth American during World War 2. On his arrival in Venice all is not what it seems and Mercer soon attracts the attention of both the Italian police, and shady underworld characters. Discovering that Ucello was apparently killed during World War 2, Mercer believes his search is at an end. However the Police take a special interest in his investigation believing that Mercer is somehow involved in a plot to assassinate a leading politican. Cold war intrigue is everywhere as the assassination plot unfolds and the identity of the sniper is a shock to the authorities!!