Biggles and 666 Squadron mount an operation against the Japanese from a secret base in Borneo. They have the services of an expatriate Englishman, Captain Larrymore, and his native allies the Punan headhunters.

goodreads summary

Biggles is asked to take 666 squadron to Borneo to fight against the Japanese from a secret airfield. Captain Rex Larrymore had discovered the airfield prior to the start of the war when he had to make a forced landing in Borneo. Larrymore has befriended the local natives, dangerous headhunters, and had set up as a prospector with a good supply of fuel and oil on this airfield, which he had named "Lucky Strike".