In Mystery on the Moor, part of the Biggles Flies to Work anthology, Doctor Alton Bentworth was a plastic surgeon who had been struck off the register for improper conduct. Knowing he needed to make a living, his school mate, former solicitor Manton Rushling approached him with a proposition. The idea was to set up a "clinic" in a remote farmhouse in Dartmoor where criminals could take refuge and meanwhile have their faces and/or fingerprints altered through plastic surgery.
Bentworth lived in London. As he needed to visit his patients in Dartmoor daily, he flew there using an Auster which he kept at the Longborne Flying Club. It was this Auster which Ginger spotted landing at the Dartmoor farmhouse which raised Scotland Yard's suspicions. When Ginger and Bertie, posing as lost hikers, visited the Dartmoor farmhouse, Ginger found a photo with Bentworth and some friends in front of an Auster. This photo later allowed the aircraft and Bentworth to be identified.
Biggles and Gaskin raided the Dartmoor farmhouse and arrested Bentworth. Bitter at having been drawn by Rushling into the crime, he turned Queen's Evidence and presumably ended with a lighter sentence.