Biggles hears from Air Commodore Raymond that Algy while in India assisting the authorities there on a gold smuggling case. More mysteriously, Algy was last seen in a Hawker Hunter which he had borrowed from the Indian Air Force. Biggles gathers the others and reviews Algy's letters to see if he left any clues about what he was up to but there was little to go on, except that he was near to cracking the case and that there were just a few details to tie up.
Biggles and Bertie set off in an Auster for Shara, a small airport in Northeast India near the border with Nepal--the base where Algy had been operating from. There they meet Mr Akbar, the airport manager and his personal secretary Bula Din. Akbar introduces them to Ram Singh, a young mechanic who had taken care of Algy's aircraft.
Ram Singh can tell Biggles little as Algy did not discuss his work much. But he did once ask Singh rather mysteriously whether he had ever seen a man with a wooden leg. Algy had also asked if Singh had ever flown over the Terai. As they walk towards the hangar to inspect Algy's Auster, they spot a man walking with a limp emerging from the hangar and Biggles worries that they have been overhead.
Biggles and Bertie prepare to spend the night in the rest-house at the airport. There in the lounge, a rather well-dressed man joins them, asking a lot of questions about their purpose in Shara. Biggles doesn't give much away and soon the meeting breaks up but not before Biggles, by means of a gentle kick, learns that the man has a wooden leg!
Retiring to their bedrooms, Biggles suggests that they move to a nearby vacant room, but first lay pillows and bolsters to make the beds in their designated roods occupied. Biggles' caution is soon justified: in the middle of the night, a scantily clad assassin climbs into Biggles' room through the window and stabs the pillows on the bed, fleeing when he discovers that nobody is there.
The next morning, Biggles' is not surprised to see the well-dressed man turn up to look them over, having, it seems, been advised by hotel staff in his pay that something seems to have gone wrong with the assassination attempt. This time, the man introduces himself as Holman Larta, a businessman in transit to Calcutta but stranded in Shara, having missed a connection.
Biggles and Bertie take off in the Auster on their first reconnaissance, inviting Ram Singh along--a trick, Biggles tells Bertie, to ensure that he had not tampered with the aircraft. Singh's enthusiasm at being invited along however, proved to them that he was trustworthy. The flight takes them to the edge of the Terai uneventfully and they return to Shara. Biggles now makes arrangements for Singh to sleep in the Auster that night to guard against sabotage but first to get himself a whistle.
In the early hours of the morning Biggles and Bertie are awakened by a whistle blast. Rushing to the hangar, they see a figure running out. They examine a bag he had dropped and it turns out to contain a venomous snake which he had hoped to plant in the aircraft. He had also dropped a pair of horn-rimmed glasses--much like that worn by Bula Din!
Biggles, Bertie and Singh make their second reconnaissance and this time, head directly north for the Terai. There, Bertie spots what appears to be a landing strip in the jungle. Biggles decides to land there to investigate. On the landing strip they discover the wheel tracks of Algy's Auster but before they can do more, they hear the engines of an approaching aircraft.
Biggles hastily sends Bertie and Singh off in the Auster, electing to stay behind to observe things. An unidentified aircraft of unknown make lands at the strip but Biggles is surprised to hear a few rifle shots which appear to strike the aircraft, forcing it to take-off again. Wondering who the mystery rifleman is, Biggles looks around but finds nothing. He settles down for a night in the jungle to await Bertie's return.
Berties comes back with Singh the next day and this time Biggles decides to hide their Auster under vegetation at the edge while they stay to watch developments. They do not have long to wait as the unidentified aircraft soon returns and rakes the landing strip with machine gun fire. This time, Biggles spots the mystery rifleman on the ground returning fire. After the aircraft leaves, Biggles ambushes him. It turns out he is Mohamad Khan, an ex-subahdar and shikari, and better still, he had found Algy when he had crashed and had been taking care of him!
Elated, they are taken to Algy who is injured but recovering. Algy fills them in on the details of the case. It seems the unidentified aircraft had been bringing gold from the north and dumping it at the strip. The connection at the Indian end was none other than Mr Holman Larta, who comes later in a de Havilland Dragon Rapide to pick up the gold, hiding it in his prosthetic leg, which was hollow. Algy had been fired upon by the unidentified aircraft and had gone to borrow a Hunter. The authorities had been warm to the idea, even suggesting that he could shoot the unidentified aircraft down. Unfortunately, Algy's Hunter had been sabotaged and had caught fire, crashing into the Terai.
Back at Shara, Biggles and Bertie devise a plan to recover Algy. Bertie would fly the Auster to pick Algy up which Biggles would fly high cover in another borrowed Hunter. The pick up is successfully executed, but just as the Auster is taking off, Biggles spots the unidentified aircraft streaking low over the jungle in pursuit of the Auster. This was the kind of trouble Biggles was half-expecting, but with a Hunter, he was well able to respond, diving after the unidentified aircraft and shooting it down.
On their return to Shara, they meet Mr Akbar who tells them that the Indian police has just made a raid; Bula Din was among the arrested, and Holman Larta had been caught with the incriminating gold in his hollow leg. The whole gold-smuggling ring had been rounded up. Happy with the outcome, Biggles, Bertie and Algy return to Britain.