It's 1959 and Russia is winning the space race. In order to compete, The United States forms NASA and chooses to recruit the nations best test pilots to form what will become the Mercury Astronauts. Among these test pilots are the golden boy John Glenn, the reckless Alan Shepard, and Gordo Cooper, whose broken marriage could cost him a place at the program.

The press descends upon the domestic lives of the astronauts. Shepard and Gordo wilt under the limelight while Glenn thrives. Glenn secures a deal with Life Magazine that grants exclusive access to all seven astronauts in return for life-altering compensation. By the time the astronauts arrive in Florida to begin work, even Shepard has come to understand the power they now hold.

After mysterious bouts of vertigo, Shepard turns to Dee O'Hara to help him. Meanwhile, Cocoa Beach has transformed from ghost town to perpetual party. Gordo finds himself tempted by another woman. Glenn seeks refuge from the bedlam at a local church gathering, where even he is confronted by temptation. The astronauts' families arrive in Florida to watch the first test launch of the Atlas Rocket.

After a rocket malfunctions during a test, the Mercury 7 head home for Christmas. Shepard's holidays are fraught, as the arrival of his parents coincides with the adoption of Louise's niece. Gordo's former mistress forces her way back into his life, jeopardizing his relationship with Trudy. And Glenn attempts to win over a rising political star and presidential hopeful, JFK.

Trudy meets with Jerrie Cobb and is invited to join the first all-female-astronaut corps. The Mercury 7 are sent to San Diego for some glad-handing, but the trip sours when Shepard is caught by a reporter with another woman. Glenn helps Shepard get the story spiked, but his moralizing drives a wedge between him and the other astronauts that will directly affect who is chosen to go to space first.

JFK sends a science committee to Cape Canaveral to assess the validity of the space program. Glenn, burning from the results of the peer vote, drafts letters to politicians complaining that Shepard is morally unfit to be the first man in space. But matters of internal power plays and a skeptical president are soon dwarfed by news out of Russia that could be the nail in Project Mercury's coffin.

On the Eve of the flight, Louise learns of Shepard's affair in Tijuana. Trudy watches Gordo crack a joke about women astronauts on television. Glenn awaits the humiliating moment when the world will finally learn he won't be first. Tensions reach a breaking point when Shepard and Glenn are forced together in a pressure cooker of weather delays, marital discord, and a circus of reporters.

After Shepard's dramatic voyage to space, he feels underwhelmed and restless. Heeding Glenn's advice, Shepard attempts to quell his ambition with gratitude for his wife and children. While Shepard's marriage somehow remains intact, Gordo and Trudy's may never recover. Meanwhile, when JFK publicly issues a challenge for NASA to send a man to the moon, Glenn's drive to top Shepard is reignited.