In Biggles in Australia, Adamsen was a Communist sleeper agent of von Stalhein's network in Australia.
Von Stalhein had turned up in Australia, ostensibly a survivor after his oceanographic ship the See Taube had been wrecked off the Northwest coast of Australia during a violent storm known as a "willy-willy". While investigating the reasons for von Stalhein's presence in Australia, Biggles and Ginger locate debris from a shipwreck on a remote island. Ginger picks up several sheets of paper. One sheet had a list of names and addresses which included Adamsen.
When Biggles arrived in Broome and called on Sergeant Bill Gilson, he asked the Australian policeman if he knew any of the names or places listed on the sheet. Gilson didn't but he noticed that Adamsen had a Perth address and offered to ask his headquarters there about him. The information from headquarters indicated that Adamsen was an agitator and trouble-maker. Gilson described Adamsen, an electrician by trade, as "a red-hot Communist of the loud mouthed type". Later in the book, he was described as a"cadaverous fellow with small dark eyes set close together and a straggling beard."
Biggles and Gilson met Adamsen when they flew to Tarracooma to look up Roth, another name on the list. Adamsen had apparently been flown there from Perth by the network's staff pilot Cozens to fix the radio. As Roth was operating the radio without a licence, Biggles had the valves removed. Gilson later arrested Roth as an accessory in the murder of Joe Hopkins but they decided to leave Adamsen alone as there was no indication that he was complicit in the crime. In any case, without radio or air transport, Tarracooma was neutralized as a base for espionage or terrorist activity. There was no indication of the fate of Adamsen at the end of the book but it can be assumed that he was rounded up with the rest of the network