Solo investigates the curious death of an air force man in Iowa with scuba gear, and with the help of Jill Denison (Katherine Crawford) uncovers a plan by Clint Spinner (Slim Pickens) to steal a missile- plane from a secret base under a farm.

In Yugoslavia, Solo and Illya are aided by Marion Raven (Jill Ireland) in stopping Gervaise Ravel (Anne Francis) and her partners from using a fear gas to overthrow various governments. While two of them are captured, two of them escape, and the story continues in "The Giuoco Piano Affair"

The conuation of "The Quadripartite Affair". Gervaise Ravel (Anne Francis) returns and Solo and Illya again enlist Marion Raven (Jill Ireland) to help them pursue her through the Andes, where the treachery of police lieutenant Manuera (James Frawley) impedes their efforts to capture Ravel.

On vacation Solo is asked by an old love interest, Clara Valdar (Madlyn Rhue) to help her smuggle Gypsy leader Emil (Jacques Aubuchon) out of Terbuf with evidence that the corrupt head of the secret police, Colonel Morisco (Alan Caillou), has been embezzling foreign aid money with the aid of the repulsive Major Vicek (Albert Paulsen).