Tyneside, 1936, the launch ceremony of HMS Invincible, the Navy's first aircraft carrier. While his daughter Celia officially launches the ship, Admiral Wetherby is sceptical of its value, claiming that it can never do the job of the big battleships. Captain Fairfax, however, insists that one day Invincible will be a crucial force.

During flying exercises, Fairfax is visited by Admiral Wetherby, Celia and her young brother Mickey, who despite his father's doubts is joining the Fleet Air Arm. The pilots - Lieutenants Stacey, Maxwell and Grant - return to base, where they are greeted by an admiring Celia and learn that they have been selected to test new aircraft. To Celia's pleasure, Wetherby invites Stacey to dinner. Stacey is wary, but Grant is smitten with Celia. Stacey has a date with an old flame, Kay Gordon, a singer, who is jealous of Celia.

Young Wetherby is caught using a flight training room without authorisation; he was given the keys by Grant and Maxwell in return for photographs of Celia. Stacey lets the boy off his punishment in return for an invitation to the Wetherbys' Christmas party. At the party, Celia juggles the attentions of the three pilots. But although Stacey expresses his love, she is more interested in Grant. Later, Stacey confides his love for Celia to Kay, who his hurt.

Portsmouth, 1937. After Stacey and Maxwell test the new fighter aircraft, young Wetherby begs for a tour. Stacey refuses, until Wetherby tells him Celia is nearby. Despite warnings that the aircraft needs repairs, Stacey takes Wetherby up. After an attention-seeking fly past the Invincible, for Celia's benefit, Stacey finds the controls not responding. He orders Wetherby to bail out before doing so himself, but Wetherby stays on board, and tries to land the plane. He fails to control it, and crashes. The boy dies without regaining consciousness; Stacey is court-marshalled.

Stacey, now a commercial pilot in the Aegean in a tiny operation run by the cheap but ambitious Papadopoulos, receives a surprise visit from Kay Gordon, who arrives with Stacey's fellow pilot, a German named Wagner. Stacey is surprised to learn that Grant and Celia are now married with a child. Kay's fellow passenger, an apparently English businessman Mr Fields, reveals himself to Wagner as an SS officer and tells Wagner to await his instructions.

September 1939. The Invincible is assigned to the Mediterranean. Grant and Maxwell petition Fairfax on behalf of Stacey, whose pleas to rejoin the Navy have been rejected. But Admiral Wetherby vetoes the idea.

Kay is subject to unwelcome advances from Wagner. Stacey returns and beats Wagner soundly. Later, on a sortie, Stacey spies the Invincible. Meanwhile, Fields takes control of the island, planning to kill Stacey on his return. Papadopoulos refuses to co-operate and is beaten; Kay warns Stacey and is shot. Stacey and his co-pilot, Matt, overcome the Nazis and Stacey finds Kay. He expresses his love as she dies in his arms. Leaving the island in the plane, Stacey and Matt investigate nearby Panteria, spying minelayers and German troops massing to support the Italians. Stacey is pursued by Wagner and crash lands in the sea, taking one Italian fighter down in the process.

Stacey and Matt are picked up by the Invincible, and report their discovery, forcing Wetherby to change plans and order an assault by air rather than artillery. Dick is greeted by his former cohorts, but must remain behind when the squadron is mobilised. The planes inflict heavy damage on the enemy base. The Germans respond with their own planes. British fighters and naval guns defend well, but the Invincible's runway is damaged; Fairfax is wounded in the process, but insists the planes should land. Two are destroyed in the process.

When another plane is destroyed on take off, Wetherby, short of pilots, calls on Stacey to join Grant and Maxwell in the assault on Panteria's dam. The torpedo attack fails, but Stacey goes on alone, ditching his co-pilot, Matt. Stacey is hit by German fire, but manoeuvres himself over a German bomber, forcing it, and himself, into the dam. Thanks to Stacey's sacrifice, the Fleet Air Arm triumphs, leaving the way clear for the infantry.