In 1962, Major Hank Marshall Tommy Lee Jones and his wife Carly Jessica Lange Marshall navigate a marriage strained by the demands of a high-stakes military career and the fragility of Carly’s mental health. Hank, a nuclear engineer, champions underground testing—codenamed Blue Sky—as a safer alternative to open-air detonations, hoping to protect people and the planet even as the pressure to choose between duty and family mounts. The couple’s move from Hawaii to a secluded base in Alabama intensifies Carly’s unrest, casting a shadow over their eldest daughter Alex Amy Locane and the entire household.
Upon arrival, Hank’s proposal meets firm resistance from base commander Colonel Vince Johnson Powers Boothe, who dismisses the underground approach despite solid scientific backing. At a social gathering hosted by the base officers’ wives, Carly’s behavior becomes a focal point of gossip and concern. Vera Johnson Carrie Snodgress urges Vince to temper the situation, but his real aim appears to be to remove Hank from the equation to clear the way for other personal priorities. Amid the tension, Alex begins a romance with Vince’s son Glenn Chris O'Donnell; on their first date, what seems like a dud grenade detonates, revealing the depth of Vince’s motives and complicating the family’s already fragile dynamics.
Hank is dispatched to the Nevada Test Site to oversee the first underground experiment under Lt. Col. Robert Jennings Michael McClendon. During the operation, Hank notices two cowboys in the testing area and pleads with Jennings to abort for their safety, but the command goes ahead, ignoring his warnings and pulling him away from Alabama. Back home, Hank learns that Vince has engineered a situation designed to sideline him, while the affair with Carly escalates and spills into a public spotlight that quickly spirals out of control. A dance recital organized by the officers’ wives becomes a flashpoint, Carly’s reaction turns volatile, and she is hospitalized after a confrontation that leads to Hank’s arrest.
Vince presses Carly to choose between a court-martial for Hank or a commitment to a psychiatric facility. Hank, intent on exposing the danger posed by the cowboys and the test, leans toward a public trial, but the scheming already seems to have ensnared him. He is transported to a hospital and heavily sedated as the wheels of the plan continue to turn. Carly, increasingly convinced something is deeply wrong, digs through Hank’s documents and uncovers the report about the cowboys, setting her on a cross-country journey with her daughters to uncover the truth.
Determined to force accountability, Carly tracks down the cowboys and learns they are suffering from radiation exposure. When they refuse to speak out, she chooses a drastic tactic: she steals a horse and rides into the test site to reenact their ordeal, a bold move that draws national media attention and puts pressure on the system to reckon with what happened. Faced with the mounting scrutiny, Lt. Col. Jennings is compelled to release both Carly and Hank, signaling a turning point in their struggle for justice.
Returning home, Hank resigns from his post, while Vince is relieved of his duties. The family, bruised but hopeful, embraces a chance at renewal as Hank accepts a new opportunity in the private sector and they prepare to start anew in California, where a quieter, steadier future finally seems possible.
