Pilot Officer Peter Penrose (John Mills) is posted in the summer of 1940 as a pilot to (the fictional) No 720 Squadron,[N 1] at a new (fictional) airfield, RAF Station Halfpenny Field. He is a very green "15-hour sprog" Bristol Blenheim pilot and is assigned to B Flight, under Flight Lieutenant David Archdale (Michael Redgrave).

When No 720 Squadron's commanding officer, Squadron Leader Carter (Trevor Howard, in his second but first credited film role), is shot down, Archdale takes over. While Penrose develops into a first-class pilot, he meets Iris Winterton (Renee Asherson), a young woman living with her domineering aunt at the Golden Lion hotel in the nearby town. Archdale marries Miss Todd (Rosamund John), the popular manager of the hotel, who is known to everyone as Toddy. The Archdales later have a son, Peter.

By May 1942, the squadron is now flying Douglas Boston bombers. When Penrose shows signs of strain from extensive combat, Archdale has him posted to controller school but is himself shot down and killed over France while Penrose is on his last mission. Penrose had been courting Iris, despite her aunt's disapproval, but Archdale's fate weighs heavily on his mind. Not wanting Iris to suffer if the same thing happened to him, he stops seeing her.

No 720 Squadron is sent to the Middle East, but Penrose remains behind as a ground controller for a United States Army Air Forces B-17 Flying Fortress bombardment group, which takes over the airfield. He befriends USAAF Captain Johnny Hollis (Douglass Montgomery) and Lieutenant Joe Friselli (Bonar Colleano). On 17 August 1942 the American airmen participate in the first attack by the USAAF on Occupied France, later ruefully acknowledging that they underestimated the difficulties involved. Afterwards, Penrose is posted to flying duties with an RAF Avro Lancaster bomber squadron.

In 1944, now a Squadron Leader and Pathfinder pilot, Penrose makes an emergency landing at Halfpenny Field, where he once again meets Iris. Iris had decided to leave her aunt for good and join up. Toddy persuades a still-reluctant Penrose to propose to Iris, saying that she did not regret her own marriage in spite of her husband's death. Hollis, who has formed a platonic relationship with Toddy, is killed while trying to land his battle-damaged B-17 with a hung up bomb aboard, rather than safely bail out and risk crashing into the local village or another town. (fonte: Wikipedia)