A rich merchant, Mr Tidore has put in an insurance claim for a large sum of money alleging that he and his pearling ship, the Shima had been robbed of its oyster catch by pirates using an aeroplance as a spotter off the Nicobar Islands. Biggles is suspicious. He surmises that Tidore must be holding back on facts like the true purpose of his voyage, the actual cargo of the Shima or even the identity of the pirates.
Biggles decides to investigate the case from both ends. He and Ginger will fly out to Ceylon in the Halifax to interview Tidore, while Algy and Bertie in the Otter will visit airfields near the Nicobar Islands to check for leads on the aircraft used by the pirates.
Arriving at Jaffna in Ceylon, Biggles and Ginger find Tidore unhelpful and they learn nothing new from him. However, on leaving Tidore's residence, they are accosted by a suave man in a white linen suit and panama hat. He does not give his name but they later learn that he is called "The Count". The Count, who represents a group hostile to Tidore, tells them that Tidore is actually a smuggler and have moved into their territory by smuggling gold from Macao concealed in oysters--oysters which they had taken off the Shima.
Biggles and Ginger decide to leave Jaffna but Tidore now insists on seeing them again. He is highly agitated to find that the Count has spoken to Biggles but Biggles convinces Tidore that it is now in his best interest to reveal all he knows about the rival gang. Tidore tells them that he has been smuggling opium into India for some time but now a rival gang has moved in and are swamping the markets. The gang, led by a mysterious man known as "The Colonel" and assisted by "The Count", uses aircraft and ships from an airfield in the Nicobar islands. This airfield, together with a large amount of stores, had been abandoned by the Japanese after the Second World War.
Just as Tidore is about to reveal the location of the base, he falls silent and when touched, falls forward, dead from a stab wound in the back. He had been sitting on the verandah with his back towards the garden. It must be the Count's gang and they are in the grounds of Tidore's house! Climbing over the garden wall, Biggles and Ginger make a narrow escape from the gang and, reaching the airport, depart in the Halifax for Kutaradja on the other side of the Indian Ocean.
Arriving at Kutaradja Airport, the traffic manager, Mr Vandershon tells them a Dakota has radioed in, asking if the Halifax had arrived. Vandershon had answered no but minutes later he receives a new message that the Dakota is coming in. Tidore had told them this Dakota belongs to the Colonel so Biggles sends Ginger off in the Halifax while he remains behind, disguised in mechanic's overalls, to get a closer look. The Dakota lands, and Biggles catches sight of the Colonel, the Count and the Japanese pilot Mitsubu. They leave again when they find the Halifax gone.
Ginger picks Biggles up after the departure of the Dakota and they proceed to the rendezvous with Algy at the airport at Kuala Lumpur. While discussing the case, they spot the Colonel's Dakota landing. Biggles sends Algy and Bertie off to take photos from concealment while Biggles and Ginger prepare for the inevitable confrontation. The Colonel and the Count approach Biggles and Ginger and, using a combination of threats and bribes, try to convince Biggles to halt his investigations. Naturally, the Colonel's efforts fail and they take their leave.
Biggles now sends Bertie off in the Otter to shadow the Dakota. It is now that Bertie plays the eccentric Englishman to masterful effect. He follows the Dakota to Kutaradja and barges in on a meeting between the Colonel and Vandershon, claiming to be cruising around the region looking for ... shark's teeth! Have they got any? Bertie's presence prevents the Colonel from completing his meeting with Vandershon and he leaves. Now Bertie follows the Dakota all the way to its secret base in the Nicobar Islands where he is intercepted by Mitsubu in a Nakajima fighter and forced to land. Confronted by the Colonel and the Count, Bertie tells them he had followed them in the hope of reaching Penang. Didn't they say they were going there? The Colonel is exasperated, but they underestimate Bertie and can't take him seriously. Bertie is allowed to leave and he returns in triumph to meet Biggles with the location and a detailed reconnaissance report of the base.
The team is discussing the next step when two pilots arrive from Kutaradja with news that Vandershon has been stabbed. This angers Biggles and he is determined to do something about it. They take the Otter to Kutaradja and, late at night, glide in to land quietly without radioing their arrival or seeking clearance. Biggles is thus able to surprise the staff in Vandershon's office where he catches the clerk trying to send a message about Biggles' arrival. The clerk is forced to confess to stabbing Vandershon and he is handed over to the police. They then depart for the island, intending to arrive while it is still dark.
Arriving at the island, Biggles, Bertie and Ginger set off on a reconnaissance which Biggles wants to conclude quickly because he notices a storm approaching. Advancing towards a cove, they spot a yacht, like the one that could have stopped and robbed Tidore's ship. Biggles sends Ginger forward to get the name of the yacht. This is easier said than done, but Ginger gets close enough to spot the name Floridia. He also takes the opportunity to cut the mooring ropes, causing the yacht to run aground in the swelling sea. But they have taken too long, and returning to the Otter, they find that Algy has taken off in order to avoid being trapped near the island by the storm.
Biggles, Bertie and Ginger move towards the airfield and spot Mitsubu and the Count leaving on the Dakota--Mitsubu obviously hoping he can outrun the storm. But minutes later, they see Mitsubu coming back--he had changed his mind and wanted to land quickly before the storm hits. But Mitsubu doesn't know the wind has shifted, causing him to botch his landing. The Dakota crashes and bursts into flames, killing Mitsubu and the Count and also destroying the Nakajima as well.
The gang without transport is good news, so Biggles thinks, but after the storm abates, they see a second Dakota landing, and who should emerge but Algy, at gunpoint! He had flown his Otter to Kutaradja and had been kidnapped by members of the gang and brought back.
Biggles decides they must rescue Algy and steal the Dakota as well. Disguising himself in the clothes of the Chinese laborers in the gang, Ginger heads for the Dakota while Biggles storms into the Colonel's office where Algy is being interrogated to demand his release. Needless to say, the Colonel doesn't give in but Biggles' boldness distracts the Colonel and his men long enough for Ginger to get away. On the downside, Biggles is himself captured, disarmed and thrown into a bunker with Algy.
Left alone, Bertie now moves fast. Reasoning that he must immobilise the gang, he first steals towards the grounded yacht and sets it on fire. This sends most of the gang towards the cove and Bertie is able to disarm the remaining guards and release Biggles and Algy.
But it is not over yet. The gang is now bent on "total war" and begins combing the island in search of Biggles, Algy and Bertie. What's worse, they see the Dakota coming back--but flown by someone else instead of Ginger. What has happened? But there is no time to reason things out--the Dakota is now loaded with bombs and begins to make bombing runs over parts of the island with the intention of flushing them out.
Biggles and co have hardly any answer to the Dakota's bombs. But just as the situation gets desperate, two large Globemasters make an assault landing on the airfield, loaded with U.S. marines, with Ginger among them! Apparently the pictures Algy and Bertie took of the colonel had greatly excited the U.S. authorities and they were determined to arrest him for fraud and other offences. So they asked Ginger to rendezvous and act as guide for General Cotter and his marines. The troops make quick work of securing the island and the gang, leaving Biggles and his crew well satisfied at having made both ends meet.