In Biggles Nets a Fish, Felceman was a sports fisherman who owned the fishing rights on the stream downstream of where it ran past the atomic research station at Heatherstone Moor. Since he lived nearby and owned an aircraft, he was a natural target of suspicion when secret microfilms of research in the station were found to have been airdropped over Germany. However, Colonel Barclay, the officer in charge of security told Biggles early in the investigation that his people had checked out Felceman thoroughly and found nothing suspicious.
After arriving at Heatherstone Moor, Biggles stretched a net across the stream and caught a capsule that had been thrown into the stream from the atomic station. After reading the message, Biggles allowed the capsule to go on its way, towards Felceman's farm. When Biggles saw Felceman's lights go on and off in accordance with the instructions, he knew Felceman was somehow connected with the spying activities.
What puzzled Biggles was that Felceman had a fine war record as a pilot of the Free Czech Air Force. Since the war, Felceman had settled down as a farmer in his newly adopted country, even changing his name to Felce. Biggles also recalled once saving his life during a dogfight when Felceman had been set upon by six enemy aircraft. Colonel Barclay also brought more worrying news that Felcemen had been seen trying to fit a long-range tank into his de Havilland Gipsy Moth aircraft.
Biggles visted Felceman's farm and confronted Felceman. Felceman he did receive items from the station which he placed inside a salmon and delivered it to a hotel in London. He didn't know who his principals were but he received his instructions there. He explained that it was not espionage: he was smuggling radium out to friends so that they could sell for money and buy their way out of communist controlled Czechoslovakia. When Biggles showed Felceman that the capsule contained not radium but microfilm, Felceman realized that he had been duped and offered to help Biggles catch the spy inside Heatherstone Moor.
Felceman had an emergency procedure--after flashing a prearranged light signal, he was to land his Gipsy Moth on the airstrip inside Heatherstone Moor to pick up the spy and escape together. With Biggles hiding inside the Moth, Felceman executes this plan and so caught the spy waiting at the airstrip, who turned out to be the deputy director Doctor Mills. Leaving Mills in the hands of Colonel Barclay, Biggles then takes him to London, in order to pick up the network's London contact.