Chapter 1: How It Began[]
While on leave and in civvies in London, Biggles is mistaken for one Captain Leopold Brunow by a talent-spotter and offered a job to work for German intelligence. Biggles reports this to British intelligence and General Pendersby asks him to play along, effectively becoming a double-agent.
Chapter 2: Algy Gets a Shock[]
Meanwhile, Algy, in France, gets sudden movement orders for the Middle-east. Cursing the stupidity of headquarters bureaucrats, Algy arrives at Kantara in Palestine with Major Raymond. Biggles is there! Following General Pendersby's instructions, he accepted Broglace's offer and had become a German agent, posing as the disgraced R.F.C. officer Leopold Brunow. He had been posted, at his request, to Palestine at a German airbase at Zabala. British intelligence wants him to identify a deadly German agent codenamed "El Shereef". Algy and Raymond are to be his liaison.
Biggles had flown out in a German-captured Sopwith Pup on a familiarisation flight from Zabala and had taken the opportunity to meet up. While leaving, Biggles spots an Arab riding off quickly into the desert. A mechanic tells him it is Major Sterne, a British agent who operates among the Arabs.
Chapter 3: Biggles Gets a Shock[]
Biggles returns to the German aerodrome at Zabala and reports to his superior, Count von Faubourg, chief of German Intelligence in the sector and his chief of staff, Hauptmann Erich von Stalhein. Von Faubourg shocks Biggles with a few pointed questions. He seems to know Biggles was at Kantara and had met Major Raymond. Biggles blurts some excuses which seem to satisfy von Faubourg but von Stalhein doesn't look convinced.
Chapter 4: A Meeting and a Duel[]
The next morning von Faubourg wants Biggles to fly a reconnaissance to find a force of Australian cavalry.
Biggles seizes the chance to fly to Abba Sud where he had arranged a rendezvous with Algy and Raymond. Raymond tells Biggles that he can report the Australian force at Sidi Arish. They would be moving out soon and would be away by the time the Germans manage to mount an air attack. Raymond then passes Biggles an explosive charge with instructions to blow up a water reservoir north of Zabala.
A Pfalz swoops overhead. It's Leffens, a German pilot who flies for Von Stalhein. He must have been sent to follow Biggles! At all costs he must not get away. Biggles gives chase and shoots him down. He lands to inspect the crashed Pfalz and finds Leffens' signet ring, similar to the one that he and others working for German intelligence were issued with. It might be useful, so he picks it up.
Chapter 5: The New Bullet[]
Back at Zabala, Biggles reports that the Australians are at Sidi Arish. At the mess, the pilots tell him Leffens is missing and that he had been trying out some new bullets which had only just arrived. Outside, Biggles spots von Stalhein poking around his Sopwith Pup. Biggles notices later that a bullet lodged in the woodwork has been dug out. So now von Stalhein knows Biggles had been fired upon by the new bullets Leffens was using!
Von Faubourg now summons Biggles and tells him that the mission to locate the Australians was just a test. There was no real Australian cavalry to be found. Why had Biggles made a false report? But Biggles is saved from further explanation: a photo-recce Halberstadt returns with photos showing the Australians really there! The count is delighted and rushes off, not giving von Stalhein a chance to mention the matter of the bullet.
Chapter 6: More Shocks[]
At night fall, Biggles plants the bomb and then rejoins the pilots in the mess for dinner.
Biggles hears an F.E.2D overflying the airfield blipping its engine. It is Algy. This was their agreed procedure to drop urgent messages for him. Anti-aircraft batteries open up but they are silenced by a sudden massive explosion and the sound of rushing water: the reservoir has been blown!
Late at night, the Halberstadts take off for a raid on the Australian cavalry. But a lone Halberstadt returns. Biggles sees an Arab walking across the tarmac and getting into von Stalhein's room. He follows and peeps through the window. Von Stalhein is alone! Could he have been disguised as the mythical "El Shereef"?
Chapter 7: Still More Shocks[]
Next morning, von Faubourg confronts Biggles. Von Stalhein has found Biggles' signet ring at the reservoir! Biggles must think fast. It must be Leffens, he says.Leffens had borrowed his ring because he had forgotten his own. He had asked Biggles to use his, from his room. What's more, Leffens acted strangely, even shooting at him perhaps out of personal spite. The count is surprised but Biggles produces Leffens' ring as proof and this seems to convince him but probably not von Stalhein.
Chapter 8: Forced Down[]
Biggles retrieves Algy's message. There is important news and they must meet as soon as possible. Biggles gets permission from the Count and borrows a Halberstadt for a reconnaissance. In the air, he spots another Halberstadt and follows it from high level but is then caught in a sandstorm. He sees a line of palm trees and hastily puts down there. After securing the machine, he moves towards the centre of the oasis to find water and is surprised to see a large group of Arabs. Von Stalhein is there and appears to be exhorting them fervently to do something.
The Arabs and von Stalhein leave. Biggles returns to his aircraft but runs into a band of Arabs who take him prisoner.
Chapter 9: A Fight and an Escape[]
Another, larger, band of Arabs attack and take over Biggles as their prisoner. They bring him to a British outpost and "sell" him to the British officer in charge. While Biggles is being led away, he sees a figure silhouetted by a light in a tent flicking cigarette ash with his forefinger, a characteristic movement which Biggles seems to have seen before. It's von Stalhein! But what is he doing in a British tent?
Biggles is handed over to a party of Arabs to be taken to British headquarters. But the party changes direction in the desert and takes him to a remote wadi where they leave him with a package. There's a message signed "a friend" and it tells him to wait. Soon, a Halberstadt turns up, piloted by Mayer, to pick him up.
Chapter 10: Shot Down[]
On the way back to Zabala, the Halberstadt is shot down in an attack which happened so fast that Biggles did not even see the assailant. Mayer is knocked out and Biggles grabs the controls and manages a crash landing in the desert.
Mayer's leg is broken and he asks Biggles to leave him and go on his own. However Biggles refuses to abandon a fellow aviator. He fashions a trolley from the undercarriage wheels wheels Mayer to the oasis where he had force landed, hoping that his own aircraft was still there.
Chapter 11: A Night Flight[]
At the oasis, Biggles sees a large force of Arabs, some four thousand strong, apparently gathering for a raid. Fortunately, his own Halberstadt is untouched, so he piles Mayer into the rear cockpit and takes off. He heads first for Kantara where he drops a message to Algy, warning of the impending Arab raid, and then flies to Zabala.
Chapter 12: A New Pilot and a Mission[]
A visiting German ace named Hauptmann Kurt Hess has arrived at Zabala with a new fighter model, a Pfalz D.III. A veteran of 26 victories, he arrogantly tells the pilots gathered around him that the enemy is easy to kill and that he intends to get his 27th victory today, his birthday. Biggles cannot abide his haughty attitude. Fortunately, von Stalhein draws him aside with a strange mission: he wants him to bomb and totally burn up Mayer's Halberstadt.
Biggles borrows a Pfalz and lands near the wreckage of the Halberstadt. He is surprised to find a British officer's field service cap inside a secret compartment. He burns the aircraft and heads for Abba Sud to meet Algy. Algy says they received the warning about the Arab raid in time and repulsed it successfully. Second, London has sent a message warning Biggles to beware of Broglace, who has disappeared. Third, a new decoy airfield had been set up southeast of Kantara ready to be bombed.
Biggles is delighted to see that Algy has a Camel. Headquarters had lent him one because a new Pfalz D.III had been operating in the sector outclassing all the British aircraft. That would be Kurt Hess, and today being his birthday, he would be airborne right now looking for easy kills. So Biggles decides to borrow the Camel.
Chapter 13: Vickers Versus Spandaus[]
Biggles finds Hess preying on an obsolete B.E.2 reconnaissance machine. As Biggles surmised, Hess lacked real ability and had only racked up an impressive score by picking on obsolete British types. Biggles saves the B.E.2 and engages Hess, shooting him down in flames.
Chapter 14: Biggles Flies a Bomber[]
Biggles reports the new British airfield to von Faubourg. The commander is delighted and organises a raid, only, he wants Biggles to lead it! Biggles is reluctant but has no choice. The raid turns out as he expected: the British had laid a trap. Anti-aircraft fire is heavy and the Halberstadts are attacked during egress by formations of British fighters. A Sopwith Camel seems intent on attacking Biggles so he fires a red flare--his recognition signal with Algy. To his dismay, the Camel disregards the signal and presses the attack rather carelessly and is shot down by Biggles' gunner.
The Halberstadts recover to Zabala. The crews are full of praise for Biggles. His red flare was, for them, the order to form a defensive circle formation and this had saved them all from the British fighters. But Biggles is despondent: Algy is dead.
The body of the dead Camel pilot is brought in for burial and Biggles goes to see it. For some reason, it isn't Algy! Biggles is so relieved that he is laughing and sobbing uncontrollably, so much so that his mess orderly thinks he is having a nervous breakdown.
Chapter 15: Ordeal by Night[]
Night falls, and Biggles, thinking von Stalhein has gone off, goes to search his room to confirm that he is "El Shereef". But he has to hide when another intruder, an Arab, also sneaks into the room. Von Stalhein returns, and the Arab attacks. Now Biggles can see that von Stalhein, far from limping as he pretends, is as agile and fast as an athlete. He beats off the Arab's attack and then shoots him dead as he flees. It's one of the Arabs who blame him for the failure of the raid yesterday, von Stalhein tells the others.
Chapter 16: Checked[]
The next morning, the Count and von Stalhein turn another surprise: the important German agent "El Shereef" has been captured by the British and they want Biggles to go to Kantara to try to rescue him. Biggles is confused but takes a Bristol Fighter there and meets Major Raymond who confirms El Shereef's capture. He shows Biggles the German secret service ring the agent was carrying. Biggles asks to see the prisoner.
Chapter 17: Hare and Hounds[]
Biggles returns to Zabala but finds himself pursued and shot at by Pfalz fighters! He makes it to Zabala and finds his Bristol Fighter has been switched: it doesn't have the white identification bar on the wing. The Pfalz pilots are apologetic. They tell him von Stalhein had suggested that they might find "trade" in the sector where they attacked Biggles. Biggles finds the Sopwith Pup engine is still warm and has an idea how the switch of his Bristol was done.
Biggles reports to the count, telling him "El Shereef" has been executed.
Chapter 18: An Unwelcome Visitor[]
Biggles meets a visitor at the camp gate: it's the real Leopold Brunow and he wants to see the count! Biggles plays for time, saying the count is away and takes Brunow to his room where he plies him with drink and then knocks him out and ties him up. Meanwhile, von Stalhein wants Biggles to help question a new prisoner: it's Algy!
Chapter 19: Biggles Gets Busy[]
Biggles uses his authority to tell the guards to bring Algy to see von Stalhein. Once in the corridor outside von Stalhein's office, and out of sight of the guards, they detour to Biggles' room where they collect the still unconscious Brunow. They carry him to the hangar and pile him into the Bristol Fighter. Biggles then sends Algy off to Kantara.
The departure of the Bristol is soon discovered and Biggles knows his bridges are burnt. But he still has one option. He had heard a Halberstadt starting up and surmised that von Stalhein would soon be departing on a night flight. So he finds the Halberstadt and tricks the pilot to leaving the plane as he is his relief. Sure enough, Von Stalhein soon steps into the rear seat and instructs Biggles to take off.
Chapter 20: The Night Riders[]
Biggles flies the course von Stalhein's pilot had given him. Then seeing that he is near Kantara, he heads for it, throws the aircraft about violently to disorientate his passenger and then lands quickly at the British airbase. He looks back with his gun but von Stalhein is not there!
Biggles finds Algy and they seek the help of Major Raymond. Biggles needs to catch El Shereef and he wants Raymond to recall Major Sterne to British headquarters.
Chapter 21:Sterne Takes a Hand[]
The British commanding general at GHQ is far from happy with the request but he puts it through anyway. Sterne turns up and the General tells him that the prisoner he brought in, Sheikh Haroun Ibn Said was the wrong man. He is not "El Shereef". "If he isn't El Shereef, then who is?" demands Sterne. From behind Sterne, Biggles produces a pistol. "You are, I think," says Biggles. "Don't move--von Stalhein."
But Sterne, now exposed as von Stalhein, moves quickly and jumps through a window and mounts a horse and gallops for the airfield. The General with Biggles and the others follow in a car but by the time they reach the airfield, von Stalhein had taken off in a stolen aircraft. The General orders an anti-aircraft battery to bring the plane down. The battery opens up and appears to hit the plane and it is heard to crash beyond the horizon.
Chapter 22: Biggles Explains[]
Over dinner, Biggles tells the General and Raymond how he worked everything out, starting with von Stalhein's shadow flicking the cigarette ash in the British HQ tent, and then later when he found the British officer's hat in Mayer's aircraft. Von Stalhein overreached himself when he tried to frame Sheikh Haroun by using a German intelligence signet ring. Rings were rare and Biggles recognised the Sheikh's ring as Leffens' and only von Stalhein had that. When Biggles flew to Kantara to try to rescue "El Shereef", von Stalhein had followed in a Sopwith Pup. He switched Biggles' Bristol Fighter with another one which did not have an identification bar. This led to him being nearly shot down by the Pfalzs on his way to Zabala but he got back and then found the engine of the Pup still warm. Later, at Kantara, a flight sergeant told Biggles that it was Major Sterne who landed in a Pup and ordered him to switch the Bristol. This last act confirmed for Biggles that von Stalhein was Sterne.
The General is delighted with Biggles' success and he wants all of them to stay on in his headquarters staff but Biggles asks to be posted back to his squadron in France.