In The Case of the Ambitious Fishmonger, Hugo Bikstein was the leader of a gang which conducted large scale poisoning and poaching of salmon from Scottish rivers which were then flown to Billingsgate Market and sold the next day. A former Flying Officer of the R.A.F., Bikstein lived at Bardswell House in Essex which was also the landing ground for an Auster B.4 which he owned.
Biggles found the ownership of an Auster B.4, a light transport, suspicious. He did not buy the explanation that Bikstein provided to the authorities: that he was an antique dealer who preferred to fly antiques home from the continent.
Subsequent investigations showed that a car registered to Bikstein dropped off loose salmon at Billingsgate Market to a fish wholesaler named Bikstein Brothers, evidently relations of Hugo. Loose salmon was suspicious as regular salmon was usually transported from Scotland in boxes. Biggles also overhead that another load would be brought in the next day.
By discreetly entering Bardswell House estate and looking into the cockpit of Bikstein's Auster, Biggles found a map with markings indicating that he used a location in the north of Scotland named Culbin Sands. Bikstein was a member of several English and Scottish flying clubs. This was probably to allow him to refuel his aircraft easily at various locations.
Biggles reported these findings to Mr Sinclair of the Scottish Fisheries Board, who organised an operation to ambush the gang in the act of loading poached salmon into Bikstein's aircraft at the Culbin Sands. Bikstein and his gang were arrested and his aircraft and car confiscated.