In The Case of the Brilliant Pupil, Lancelot Seymour was a hardened criminal, well-known to Scotland Yard, who caught on to the idea of using aircraft in crime.
Born Hubert Roland Gestner, and later called "Toff" Gestner, he was, as Gaskin described, the sort of person who seemed to turn to crime by choice. His parents were well-off and put him in a good school but he got himself expelled for theft. He then joined a tough gang and ended up on Borstal. By the time he turned thirty, he had served three prison sentences. At thirty one, he had another three year term for forgery. He then went to Canada, ostensibly to start a new life.
Gaskin spotted Gestner back in London some twelve months later. He was now going by the name of Lancelot Seymour and, to everyone's surprise, was learning to fly at the Home Counties Flying Club in Sudbury where he was a very popular and well-liked member. Enquiries with Canadian authorities showed that Gestner had already learned to fly in Canada, had a licence and was apparently graded as a top pilot.
In Britain, at the time he came to Gaskin's attention, he already had his "A" licence and was working for a "B" (Commercial Pilot's) licence. Put together, Biggles thought the facts didn't just "smell phoney", they stank. Seymour's quest for a "B" licence puzzled Biggles as he could have flown solo and done his criminal deeds with an "A" licence. Then it occurred to Biggles that in qualifying for a "B" licence, a pilot had to perform a night cross-country solo flight. During this time, he could land or divert for a short while without anyone noticing. Enquiries with Tommy Clewson, the secretary of the flying club revealed that Seymour had failed his night cross-country flight once and was due to retake the test soon--this time a flight from Sudbury to Lympne.
Biggles decided to go down to the flying club and watch Seymour as he took off in his de Havilland Tiger Moth. Just as Seymour was about to take off, his chauffeur rushed forward with a brown paper parcel which he said was Seymour's pajamas. When Biggles stepped forward and asked to see the contents of the parcel, the chauffeur turned to run but was tripped and restrained by Ginger with the help of two club mechanics. Seymour expostulated but Biggles brought him into the clubhouse nonetheless and had the parcel opened, revealing the contents: a small parachute, and a large quantity of treasury notes, stolen from the Euston-Crewe express. He had apparently planned to divert during his flight and drop his parcel somewhere over France. The chauffeur turned out to be a man wanted by Scotland Yard, Tod Mills. Seymour was arrested by given a three year sentence.
Seymour turned up again in a second story, The Case of the Fatal Ruby where he now had the name of Captain Carson.
- In the second story, Ginger mentioned that Seymour had shaved off his moustache and this had him foxed for a while. In actuality, when Biggles and co. first encountered Seymour in the The Case of the Brilliant Pupil about three years earlier, Seymour was already without a moustache. Gaskin had said that when he described his encounter with Seymour: "It was the Toff--without the nifty moustache he used to wear." Biggles and co. had never seen Seymour with a moustache.