Spring 1915: 18-year-old Alan Farmer, a blacksmith from Becket’s Hill in Sussex, lives with his widowed mother, his father having been killed attempting to fly an old plane. Alan continues to have a keen interest in flying and engines and, against his mother's wishes, goes for an interview with the Royal Flying Corps. His father's brother, who has lost an arm on active service, comes to stay with the family and run the smithy. A local farmer's daughter, Lorna Collins, is in love with Alan but he is slow to begin a proper relationship with her. At his interview for the RFC, Alan meets Charles Gaylion, an army officer from an upper-class background who hopes to transfer to the RFC. Alan's interview goes badly, and it is clear that his working-class origins will interfere with his aspirations; however, when he mentions his past "experience" with his father's plane, he is accepted. Alan and Charles are reunited at the training centre, where they meet their instructor Captain Triggers, at first sight a bad-tempered disciplinarian. Mistakenly believing Alan to be an experienced pilot, Triggers takes him up in a dual-controlled Avro which Alan proves unable to land. He is berated by Triggers for risking both their lives. As Alan is packing his case, expecting to be dismissed, Triggers unexpectedly returns, makes encouraging remarks to Gaylion, and insists on Alan taking another flight, this time with Triggers at the controls. He performs advanced manoeuvres that leave Alan feeling foolish, but ends by telling him that he can continue with his training.

April 1915: Alan Farmer's training is well-advanced, and he shares accommodation with Sergeant MacIver, who already has experience of service with the RFC in France. Alan has had to spend time doing basic army training, whilst Charles Gaylion has already been able to complete his pilot training. Gaylion comes to visit, immediately prior to leaving for France, and now adopts a dismissive attitude towards Captain Triggers' training, particularly to the advice he has been giving Alan and the others about how to defend themselves. Charles believes that there should be honour and chivalry between pilots and is shocked to learn that Triggers and Sergeant MacIver once destroyed a German plane before it had taken off. Alan and Charles quarrel before Alan goes home on leave. Before Charles leaves, MacIver explains the circumstances surrounding the killing of the German pilot, and Charles learns new respect for Triggers, who sees him off with regret and concern. While Alan is visiting his family, his relationship with Lorna begins to get more serious. His Uncle Harry quarrels with the blacksmith, Tom, about the raising of charges in the smithy, much to the disapproval of Alan's mother, but the two men make up their differences. During a training flight, Alan's plane stalls on take-off, but he remembers Triggers’ advice "not to turn back" and crash-lands the plane in a field. The plane bursts into flames, but MacIver and Triggers rescue Alan from the wreckage. His training complete, Alan receives his "wings" and leaves for France.

May 1915: Alan arrives at ‘C’ Flight in St Marie, France and faces resentment from some officers because of to his background (‘A blacksmith? We are getting desperate for chaps’), but quickly wins over his CO, Captain Dornish, and is delighted to be reunited with his friend Charles. Following the death of another NCO on the day he arrives, Alan, initially sent out as a "spare" pilot, is sent on a mission to range for the artillery, in the company of Lt Richard Bravington, an experienced Observer officer. When they are attacked by a German plane, equipped with a machine gun, Bravington is wounded. Alan fails to follow Bravington's instructions correctly, and lands the plane behind enemy lines. However, he uses Bravington's rifle to fight off an attack by approaching German soldiers, thus winning Bravington's regard. At home, Alan's mother is invited to the cinema by the local grocer, Mr Rudkin, and Harry appears jealous, until she reveals that she has turned down a second invitation because she is not romantically interested in Mr Rudkin.

June 1915: ‘C’ Flight is ordered to locate a German Howitzer so the artillery can attack it. Alan volunteers, but Captain Dornish insists on carrying out the task himself, taking a newly-arrived observer, Guthrie, on the mission. When they fail to return, a new Flight Commander is required. Charles Gaylion is obliged to become acting CO until a replacement is appointed: Captain Triggers. When his plane fails en route, Triggers finds himself waiting at the railway station with a wounded Infantry Officer, where he learns the horrible truth of Dornish’s fate: shot down by British troops who resented having their positions given away to the enemy. Back in Sussex, 17-year-old Richard Hollis, a member of the local gentry, has been inspired by Alan's progress in the RFC and visits Mrs Farmer regularly to borrow Alan's books on the subject.

June 1915: On his arrival at ‘C’ Flight, Triggers' forthright manner and unusual ideas quickly make an impression. Seeing the inadequacies of the planes, Triggers encourages the pilots and NCOs to put forward ideas for improvement. Alan Farmer and his Observer, Bravington, get into trouble for firing a pistol to warn another British plane of the approach of a German plane, but this leads to a new strategy. Corporal Morgan, eager to win a weekend in Paris promised by Triggers, comes up with several ingenious plans for improving the plane's performance, but it is Alan who has a startling new idea that may help turn the tide. Back in Sussex, the Army begins recruiting in the village. Richard Hollis's grandfather, Sir John, leads the effort, and Lorna assists by playing the piano. As men come forward to volunteer, Harry receives news from Molly that Richard has been killed in an accident, during his first solo training flight.

June 1915: With hot weather and a break in the bombardment, Alan goes swimming and Morgan experiments with fitting bombs with parachutes. The RFC are summoned to assist in a new initiative, and Gaylion gets a taste of the horrors of life in the trenches when his plane is forced down and he must wait overnight for the arrival of a replacement propellor. He observes the demoralising effect of trench warfare on an infantry battalion and on their commander, Captain Carey. Alan convinces Triggers to allow him to transport the spare propellor on the Avro. Triggers brings Gaylion back to base while Alan fits the replacement propellor and, with Carey's help, takes off in Gaylion's plane; as he is leaving, he sees Carey killed by shell fire. On return to base, he finds that Corporal Morgan has been killed by one of his own bombs. Triggers and Alan both blame themselves for Morgan's death. Remorse, and the thought of Morgan's family, lead Alan to write to Lorna, breaking off their engagement. Alan and Charles visit a brothel where they become very drunk and start a fight. Triggers receives a complaint from the authorities, but protects the men's identities to save them from punishment. The next day, Alan flies with Bravington and is hit and wounded in the leg by their "favourite Hun" - the German plane equipped with a machine gun.

July 1915: Following his accident, Alan has to spend three weeks acting as Charles Gaylion's observer. His friendship with Gaylion causes unrest among the NCOs because of the difference in their rank, and becomes a concern for Triggers. Alan and Charles are sent back to England to pick up a new plane from Farnborough. Charles, being an officer, travels first class, but Alan is forced to stand in a crowded compartment with the other ranks. On arrival, they learn that the plane is not ready; while they are waiting, Lorna comes to see Alan at the factory. He tells her that they are both changing and he finds it difficult to plan for the future, but agrees to continue to write to her. While staying overnight at the Gaylions' home in London, he is introduced to Charles's sister Kate and her pacifist friends. Having slept until evening, he gets ready to go out with Charles but finds that only Kate is in the house. They have supper together, and Kate tells Alan that Charles has developed a drinking habit because of his fear of being at the Front. Charles returns, drunk and furious at finding Alan and Kate alone together, and creates a scene. On their return to base, Triggers is at first relieved to see that they have fallen out, but later reproves both of them for their conduct and tries to explain the need for "structure on the ground".

July 1915: Although they have not made up their quarrel, Alan and Charles are forced to continue flying as a team. Ordered by Triggers to continue with reconnaissance and to avoid the enemy, they are anxious to do something about the German plane that has been causing them so much trouble, particularly after it shoots down Charles's friend Lt Favell. Charles devises a method of fitting a Lewis gun to their plane, which Alan carries out, using his metalwork skills. They take on the enemy plane but only just get home in one piece when Alan shoots out the struts of one wing of their own plane. Only when Triggers himself is almost shot down by the German machine-gunner does he agree to allow the use of the Lewis gun to be attempted, and orders them to accept a written challenge from the Germans who wish to renew their duel "with our gallant enemy". This time they meet with better success, but Alan, having shot the German gunner, pretends the gun has jammed rather than kill the pilot as well. Back at home in Sussex, Mr Rudkin and Harry take Molly for a picnic and privately discuss their mutual feelings for her. Lorna continues to pine for Alan, and arranges to work evenings as a nursing assistant at a local convalescent hospital.

July 1915: Alan helps Charles to capture a German plane and its crew but is not invited to the meal in their honour in the Officers’ Mess that evening. Triggers is also unhappy at the two German officers being entertained, but follows the lead taken by his CO. After the senior officers have left, the remaining drunken officers indulge in horseplay and fail to keep close watch on the prisoners, who make an escape attempt. Alan, who is out shooting game, thwarts the Germans’ escape attempt. Rather than give him a commendation (which will expose the officers’ negligent behaviour), Triggers allows him a 48-hour pass to Paris where he calls on the Gaylion family and meets Charles's sister Kate again; they go out for dinner and dancing, but Alan is disappointed when Kate refuses to make any firm arrangement to see him again. Triggers is desperate when ‘C’ Flight is ordered on a suicidal mission to bring down a German kite balloon, despite the shortcomings of their planes, and Alan and his observer narrowly save Charles from being shot down. They hit on the idea of flying over the German lines in the captured enemy Albatros, and successfully bring down the balloon, but once again Charles gets the credit from his fellow officers, whilst Alan receives a dressing-down from Triggers for the unsporting manner in which it was achieved.

August 1915: Charles Gaylion's plane is set on fire despite him not having sighted the enemy. Triggers receives information about increased casualties among British pilots and he, Charles and Alan Farmer puzzle over the source of the danger. A new arrival, Lieutenant Conrad, makes few friends because of his superior attitude, but his superb eyesight becomes an advantage when he sees that what Charles and others have mistaken for a French Morane is in fact a German monoplane. Back in England, Lorna has volunteered to be a nurse and is looking after injured pilots; she begins to realise the dangers Alan faces. Triggers is frustrated that his superiors do not believe their planes are being outclassed by the Germans but his frustration turns to anger when a magazine sent to Alan by his mother provides the answer: the Germans have developed a machine gun that can fire through the propeller. With Farmer and Conrad as back-up, he lures the German monoplane into attacking him until it is driven off by Conrad with a hunting rifle, giving him the evidence he needs to alert the rest of the RFC.

August 1915: The arrival of the new German monoplane forces Triggers to order the pilots of ‘C’ Flight to fly in pairs. Despite having been wounded in the right arm on his previous flight, he returns to active service and, while awaiting the arrival of replacements for a crew killed by the monoplane, he insists on flying a routine reconnaissance alone; he and his observer go missing. Charles Gaylion is obliged to take over as temporary commanding officer, and sends Alan to photograph a German artillery dump with his observer, Conrad. When faced with the Eindecker and ordered by Conrad to move closer, Farmer turns for home and avoids a confrontation. Back on the ground, Conrad insists Farmer be court-martialled for disobeying an order and cowardice in the face of the enemy. Gaylion has no power to prevent the court-martial but succeeds in ensuring that the presiding officer has experience of flying. He agrees to represent Farmer as the "prisoner's friend" but his inexperience soon shows. At home in Sussex, the local vicar reveals the news about the court-martial to Molly, thus incurring Harry's displeasure; Molly writes to her MP to try to get help for Alan. Even after the removal of Conrad from the courtroom for arguing with the presiding officer, the court-martial is going badly for Alan, who admits to having disobeyed a direct order. As Charles begins his concluding speech, the proceedings are interrupted by the arrival of a bedraggled Triggers, who has escaped from a German field hospital after being shot down ten days earlier. His evidence is critical to the outcome of the court-martial. Alan is found guilty of disobeying an order but not guilty of cowardice, and is given a minimal sentence. Charles remains devastated at his own inadequacy as counsel for the defence.

Shortly before Molly's birthday, she receives the good news about Alan's acquittal. Following the court martial, Conrad demands a different pilot but Alan insists he wants to carry on flying with the same observer, admiring Conrad’s bravery. Conrad is unrepentant and, despite being ordered not to look for trouble, orders Alan to fly slightly off-course in the hope of engaging the German monoplane. When Alan is tempted to disobey, Conrad threatens him with his revolver. Conrad manages to shoot down the Eindecker but is fatally wounded himself. Triggers is angry when Alan writes up the full detail of the incident, and insists on his rewriting his report, hinting that a commission may be in the offing. Mr Rudkin proposes to Molly. When she refuses him, he decides to join the infantry, anticipating the introduction of conscription. While teaching Molly to ride a bicycle, Harry betrays his own feelings towards her. Charles comes to tell Alan he had been granted a week’s leave and finds him writing to Kate; he warns Alan that she will treat him badly. On his return to Becket's Hill, he intends to stay for only a few days then go to London to see Kate, but, when he telephones her to make arrangements, she makes it clear she is not interested. Gossip and bad feeling against the Farmer family surface among some of the local people, and Harry and Alan get into a fight when local youths mock the RFC. On meeting Lorna again, Alan finds she has matured, and they begin to rekindle their relationship.