As Pilot Officer Maude Garrett (Chloë Grace Moretz) arrives in Samoa with a top-secret package, she encounters skepticism from the diverse Allied aircrew aboard the B-17 bomber, aptly named "The Fool's Errand." Initially, they are dismissive of her presence but begrudgingly allow her onto the aircraft. Maude, feeling the weight of their scrutiny, finds herself confined in the empty Sperry ball turret, reluctantly handing over her document valise to the only crew member who is supportive, USAAF dorsal gunner Walter Quaid (Taylor John Smith).
As the bomber takes flight, Maude's sharp instincts detect an aircraft hidden in the clouds, a claim confirmed by navigator Bradley Finch (Joe Witkowski). In a mocking tone, both pilot John Reeves (Callan Mulvey) and RNZAF co-pilot Anton Williams (Beulah Koale) question her observation skills. However, Maude isn't just experiencing mere illusions; she's spotted a remarkable sight—a winged creature clinging to their aircraft's surface. Despite mostly receiving ridicule for her revelation, Maude finds an ally in tail gunner Stu Beckell (Nick Robinson), who supports her account.
When Maude finally escapes the confines of the turret, she becomes trapped due to a malfunctioning hatch. Frustrated by the crew's indifference, she reacts with fury, only to be ostracized further when they cease their attempts to release her and cut off her intercom. In a daunting moment, she spots a Japanese aircraft darting into the clouds, signaling impending chaos.
Amidst the confusion, a menacing gremlin appears out of the shadows, launching a brutal attack on Maude. Injured and disoriented, she finds herself prey to this creature until she taps into her inner strength to retaliate. While the crew is preoccupied with their own dilemmas—most notably questioning the very existence of Maude—she faces her tormentor head-on. Realizing she must defend herself, Maude thwarts their efforts to extract her from the turret and makes the bold decision to jam the gears, readying for an impending conflict.
Suddenly, a Japanese fighter returns, unleashing a hail of gunfire. In that adrenaline-soaked moment, Maude switches to an American accent, takes command of the turret, and heroically downs the enemy aircraft. The crew, astonished by her bravery, slowly begins to respect her—a small yet significant triumph amidst the surrounding turmoil of war.
As tensions escalate, Maude's true identity as a member of the WASP (Women's Auxiliary Service Pilots) comes to light, and she reveals that her marriage is tumultuous. Opting to board the plane under her maiden name, she keeps the specifics of her mission shrouded in secrecy. However, hints of her troubled past linger, especially as the relentless gremlin continues to wreak havoc, with Tommy Dorn (Benedict Wall) barely registering its presence.
Safeguarding her cover becomes crucial when Captain Reeves suspects that Maude's assignment is linked to their mounting troubles. When a mysterious bag surfaces, its shocking contents—a child belonging to Maude and Sgt. Quaid—force her to confront the painful truth of her life choices. A bitter affair with Quaid, stemming from her abusive marriage, leads her to fake her mission in an effort to escape her husband's wrath.
Just as Captain Reeves decides to return to base, three Mitsubishi A6M Zero fighters launch a surprise assault, affording the gremlin an opening to board the bomber and injure Quaid while abducting the infant. As the creature emerges with its prize, Maude resolutely takes action, exiting the turret and firing her handgun in a desperate attempt to rescue her child. With the bag precariously dangling from an engine nacelle, Maude makes the daring choice to crawl under the wing to retrieve her baby and reboard the aircraft through the compromised turret hatch.
The gremlin's relentless pursuit resumes, yet Maude's resolve is unshakeable. As Reeves, Finch, and Dorn find themselves under fire from Japanese machine guns, Maude rises to the occasion, skillfully orchestrating a controlled crash landing of the damaged bomber. Just when she thinks the threat has passed, the gremlin resurfaces to seize the child once again. In a final act of courage, Maude eliminates the creature, securing her child's safety. As the remaining survivors witness the catastrophic demise of The Fool's Errand amid flames and explosions, they are left to grapple with the destruction and devastation left behind.
