Ginger spots Von Stalhein entering the Grosvenor Hotel near Victoria Station. With the help of Inspector Gaskin and his CID surveillance specialists, Biggles learns that the former German secret agent is spending most of his time at Caterham, attempting to chat up British servicemen stationed at the Guards Training Depot there.
Among the soldiers is one Guardsman Ross. Through his superiors, Biggles questions Ross and discovers that Von Stalhein has been attempting to recruit soldiers for an International Brigade, promising good pay and conditions. Ross's colonel confirms that there have been seven desertions in the last three months, including a friend of Ross, Hugh Macdonald. Biggles wants to find out more and so plans for Ross to insert himself into Von Stalhein's scheme as a stool pigeon, promising to follow close behind and rescuing him when enough has been learnt.
Accordingly, Ross pretends to take up Von Stalhein's offer and is sent by a commercial service to Paris wearing a special spotted tie as an identification. Biggles, having purchased the same tie for himself and Ginger, flies ahead to Paris. His tie works and a German named Stresser opens up to him, telling him their next stop is Prague. Stresser is in Paris to escort Ross. Biggles, playing along, says he is receiving Ginger, who is also flying in from London with Ross.
In Prague, Biggles and Ginger take up rooms at the same hotel as Stresser and Ross. Next morning they try to follow when Ross is packed off to the airport but are delayed by a garrulous Stresser. They get to the airport just in time to see Ross departing on an aircraft to an unknown destination. Before they can plan the next move, who should Biggles accidentally bump into but Von Stalhein arriving on a flight! Biggles and Ginger dash out of the airport terminal and steal a car to make a quick getaway but find road blocks all over the city. Biggles decides to take a risk--they abandon the car and go back to their hotel on foot, gambling that this would be the last place the police would look. At the hotel, Biggles finds Stresser and successfully loosens his tongue with a generous bribe--Ross it seems, is headed for Kratsen, in Manchuria near the Northh Korean border to work at a propaganda station but on the way, he will be stopping by Berlin to see Hugh MacDonald.
Leaving the hotel, Biggles and Ginger evade patrols and make their way to a British intelligence safe-house whose address they had been given for emergencies. Run, it seems, by a Czech tailor named Johnann Smasrik, he turns out to be a Englishman named Smith. He knows a field which can be used for a landing and offers to send a message to Algy about a pick up. He also arranges a farm cart to take Biggles and Ginger to the field by night. All seems to go well but just before the appointed departure time, the police arrive at the door and Biggles and Ginger are forced to escape up the skylight of the attic onto the rooftops where they make their precarious way from house to house until they get to the ground some distance away. Again they narrowly evade a cordon set up by Von Stalhein and are just in time to jump on the farm cart as it proceeds on its way.
At the landing field, Biggles and Ginger spot troops laying wires to trap any aircraft attempting to land. But Biggles and Ginger are equipped with escape kits which include wire saws and they go to work cutting the wires. They finish just in time and signal Algy and Bertie down in their Proctor. They hop on board quickly and the Proctor takes off again, just as the troops lying in ambush open fire.
The Proctor makes its way to Berlin, where Biggles calls on a Major Boyd, a British intelligence officer to borrow a guide who can take him into the Russian sector without going through any checkpoints to the Hotel Prinz Karl at the Zindenplatser--the hotel Stresser said Ross was going to. He makes it there without incident but in the lobby he bumps into Von Stalhein again! Playing for time as they each play their next move, they have a few moments to sit down and talk. Biggles takes the opportunity to plant ideas which would have reverberations in future books--he asks why Von Stalhein now works for a power which he had regarded with abhorrence. Von Stalhein concedes with a sigh that he is not always the master of his own fate, whereupon Biggles promises to convince him at a later time that "tea tastes better" on his "side of the fence." In the meantime, Von Stalhein tells Biggles that he has taken the precaution of sending Ross and MacDonald on to Kratsen as he had been expecting Biggles at the Prinz Karl.
Seizing a moment when the lift attendant is not in the lift, Biggles flicks a newspaper at Von Stalhein, leaps over the sofa and dashes into the lift. He takes it up a few floors where he finds an unlocked room. There he steals a Russian officer's cap and coat. Now disguised as a figure of authority, he makes it onto the street, picks up his guide, and escapes into the British sector.
Back in London, Biggles persuades his superiors to allow him to attempt a rescue of Ross from Kratsen as well as sabotage the propaganda site. Approval is granted and Biggles calls on Gimlet and his former commando troop of the King's Kittens to join him. Biggles also asks for help from an old acquaintance, a Chinese doctor named Wung Ling because he needs someone who can blend in with the local population to reconnoitre Kratsen before the rescue operation is launched.
The team head out for South Korea in a Short Seaford which Johns calls a "Scorpion". From there, Biggles heads out Kratsen and drops Wung Ling over Kratsen by parachute for a reconnaissance, picking him up three days later. Wung Ling performs his mission spectacularly, for not only does he return with detailed knowledge of the camp layout of Kratsen, he actually spoke to Ross to alert him that friends are near.