In The Flying Crusaders, Sir Giles Mancroft was one of the early pioneers of aviation. Among his achievements was an early attempt at crossing the channel in an aircraft named "The Flying Crusader". According to Biggles, with a bit of luck he might have succeeded and would have beaten Bleriot to the feat. When he became too old to fly, Sir Giles spent his money building up a collection of vintage aircraft which he kept in flyable condition at his residence, Mancroft Castle.
In August 1939, Sir Giles had thrown a house party for some aviation enthusiasts. During this event, a valuable painting, also named "The Flying Crusader" had gone missing under mysterious circumstances. Connected with this loss, an American house guest named Joseph Silberman had been involved in a scuffle with the butler in the hangar where the "Flying Crusader" aircraft had been kept. The butler died of his wounds sustained in the fight without regaining consciousness. Silberman was hospitalized for some time and told police that he believed the butler had stolen the painting and was trying to escape with it. A search for the painting was made without success.
After the Second World War, financial difficulties forced Sir Giles to auction off most of his collection of aircraft. Biggles attended the auction at the request of Smithers, the son of the butler and while there, uncovered a scheme by Silberman to buy the "Flying Crusader" aircraft using a U.S. Air Force sergeant named Galton as a front. It turned out Silberman had stolen the painting and had hidden it in the cockpit of the aircraft. Silberman was arrested and the painting recovered. A cipher on the back of the painting led to the discovery of a hidden compartment of expensive jewels in the frame of the painting. The sale of these gems raised enough money to allow Sir Giles to keep his castle as well as the "Flying Crusader".