Keston had stolen an aircraft from Lotton Flying Club and had flown to Charmentray in France. He had burst a tyre in a night landing there and had been arrested by the French police. Extradited to Britain, Keston told the court that he have always loved flying but have never been in a plane before and had stolen one for a joyride. A judge had sentenced him to a month's jail, a lenient sentence because he considered it a sporting effort to fly without lessons.
Marcel was however sceptical and showed Biggles the narrow field in surrounded by woods into which Keston landed his his aircraft. Biggles agreed that it was far too difficult a feat for an untrained person and looked up Keston in prison. Keston admitted that he was a student for a commercial pilot's licence who had run out of money. At Lotton, he had met a man (later discovered to be Caulder) who bet him fifty pounds that he couldn't fly to France. To prove he had been in France, all Keston had to do was deliver a packet to a friend of his in France, pick up another packet from him and then fly back to Britain with it. Keston accepted the bet but had burst a tyre upon landing.
Noting that Keston seemed to like bets, Biggles makes a wager with him that he would never get the money he had won for flying to France. Keston agreed to the wager, stating that if he received the money, he would not betray his contact but if the money was not forthcoming, he would cooperate with the police.
Two weeks later, Keston told Biggles that he had won and agreed to help Biggles apprehend Caulder. Biggles noting that Caulder was an American, and that Lotton was near an American camp, postulated that Caulder might repeat the tactic and operate at other clubs near other American camps. He instructed Ginger to take Keston to clubs around Britain looking out for Caulder. This strategy succeeded. Ginger and Keston spotted Caulder at Cliverton. Ginger, working undercover, got Caulder to make the same arrangement with him as with Keston. Biggles and Marcel next laid a trap which resulted in both Caulder and his French associate being arrested.