The Rietti Group were Italian resistance fighters in the second world war helping the allies.
They were led by the aristocratic Count Montesco (Geoffrey Keen) and Ricco Poccari was part of the group. They had a signature whistle to help identify them.
They have an annual reunion dinner but they are now down to just five men from the group. The reunion is due to be held at Poccari's hotel.
However Poccarri comes across two allied paratroopers who recognise the tune Poccari whistles. They tell him a story of betrayal by someone from the Rietti Group.
It leds to their entire unit being shot dead, they were the only two survivors. Poccari has no option to invite the men to the reunion dinner as they can still recall the voice of the traitor.
A decent enough story with the Count as the main suspect as the traitor. With Poccari making phone calls to New York for some fact finding, I found the twist was effective enough.