After a failed attempt on her life, Gabrielle escapes from Paris with the help of her associate Werner Werber. Chief Supt. Franks looks into a crash-landing of a plane in Edinburgh, piloted by Werber, who was found dead.
French intelligence send pictures that show Werner Werber acting as Gabrielle's bodyguard, and she is likely to be the mystery passenger on the plane that landed in Edinburgh.
Capt. Aubrey Percival from SIS takes over command of the case. Franks discovers Gabrielle was a Soviet agent but is disillusioned. Constant Delangre the hit man is already on her tail in Scotland.
Chief Supt. Franks is under pressure from Special Branch while Captain Percival is playing politics. Franks finds and warns Gabrielle that a hit man is on her tail.
Special Branch takes over the protection and surrounds Gabrielle's home. Franks' men track the hit man down to a caravan, but he murders two people and slips the net.
Assassin Constant Delangre is shot dead by Capt. Aubrey Percival, before Special Branch arrives with the evidence that Gabrielle's housemate Agatha is actually communist agent, who will stop her leaving for Canada.
