It is 1939. Biggles, Algy, Bertie and Ginger arrive in Cairo on board two De Havilland Dragon Rapide aircraft. They have taken on jobs as flying instructors to train pilots for the Egyptian Air Force. Bertie is, as always, looking forward to the smells of oriental perfumes, the deep waters of the Nile and the caravans through the desert. The others are not so optimistic.
They are invited to a reception at the German embassy where the British governor asks to see him privately. The Germans want to build an alliance with the new King and are trying to undermine the prestige of the pro-British prime minister by arming bandits in the desert. Biggles' role as a flight instructor is the ideal cover. He can use his training sorties to check what the Germans are up to on the Sudan-Libya border.
Back at the reception, Biggles meets Heike von Kleep, a German archaeologist. She introduces him to some German embassy officials, Obersturmbahnfuhrer Botho von Ettal, the SS head of embassy security and Ottmar Strupfler, chief advisor to the ambassador. Strupler, in particular, expresses a lot of curiosity about Biggles' Dragon Rapides, especially their modifications.
Biggles joins Algy and the others and they take a walk in the garden. There they find a man almost unconscious on the ground, gasping for help. Biggles brings his car around and they secretly bring him out through a side exit and back to the safety of their hotel.
The man is Kamal el Melen, an Egyptologist at Cairo University and an expert of the 18th dynasty. He tells them how he had found some old papyrus scrolls in a tomb which mentioned the position of a lost oasis near the Sudan border. After the death of the Pharoah Akhnaton, his army. priests and followers had carried away a part of his treasured and disappeared into the desert to this oasis which was thought to posses the "Secret of Life and Death". The German archaeologists working near Kamal's dig sohehow learnt of this. They kidnapped him and imprisoned him in a cellar in the embassy and tortured him for the secret of the papyrus but he had escaped into the garden.
Biggles now tells the others the secret mission the governor had assigned to them. And it links up with Kamal's story. Perhaps the Germans had already begun searching for the oasis at the Sudanese border.
The next day, Biggles, Bertie and Kamal depart in one of the Dragon Rapides for a reconnaissance. After some time, the engines begin to run rough and Biggles puts down on the desert. Their tanks have been sabotaged and are almost empty. And the radio does not work. With their remaining fuel, they try to reach the closest oasis but hit a sandstorm on the way. in bad visibility, they seem to reach a mountainous area where Biggles attempts to land in a wadi. They get down safely, mostly intact except for a damaged propellor.
They push on towards some mountains where they find a pool of water. Then, a surprise. In a nearby cave is an aviator's suit with papers identifying it as belonging to one Waddington, an Australian pilot believed lost while crossing the Sahara in 1927.
After overnighting in the cave, Biggles and the others explore the surrounding area and discover Waddington's crashed Avro Anson. There's supplies inside and Biggles thinks one of the propellors can be used to replace their damaged one. Meanwhile Kamal is all excited: he has found ancient Egyptian weapons from the 18th dynasty. Akhnaton's treasure must be nearby!
Back at the cave, Kamal says he has discovered more weapons of the same style but of a more recent make. It's weird. Also weird, says Bertie, is that the smoke from their fire is being drawn deeper into the cave. It must lead somewhere.
They push through the cave passage and come into a vast catacomb full of mummies. According to Kamal, it's like Deir-el-Bahari, only ten times bigger. In a sarchophagus, Kamal discovers a mummy with a royal insignia showing he was from the army of Akhnaton. They meet a figure who is wrapped in bandages like a mummy. He sees them and runs off. Biggles calls to him and then follows. He is the only one who might know the way out of the complex. They almost catch up with him when everyone is attacked by a swarm of bats. They attempt to evade by crawling through a hole in the wall and end up falling down a chute.
Bertie strikes a match. They are in another chamber full of mummies. Kamal keeps muttering about ancient curses but suddenly yells: "The light, the light!" Biggles wants him to pipe down but Kamal is right, there is a light. It's a hole high up. They climb up and emerge in front of a massive temple.
Kamal is jubilant. A temple the size of Abou Simbel in the middle of the desert and he has discovered it! Biggles reminds him to be cautious. They are not alone there.
There are strange things inside the temple, or perhaps they should have expected it. A mummy chained and hooked up for some chemical experiment, and crates and crates with swastikas on them all full of rifles and machine guns.
It looks like the Germans had got there before them. But Biggles reasons that this means they have transport--they should hang around and perhaps steal one of their trucks or planes.
Too late. Von Ettal and Heike now appear with pistols in their hands. Biggles and Bertie move swiftly to disarm both of them and everything seems under control but then there's a strangely familiar voice behind them....