In 1930s Los Angeles. Jack Parsons works as a janitor at a chemical factory by day, but, by night, he nurses a secret ambition: to build rockets that will take mankind to the moon. The pressures of his double life are further complicated when Jack and his wife Susan are confronted by a mysterious new neighbor, Ernest Donovan, who appears to be leading a double life of his own.
After Jack and Richard get Professor Mesulam's permission on the project, they put together a rocket team at Caltech. However Caltech places many caveats to the program. Their neighbor Ernest add tension to Jack and Susan's lives.
Feeling the pressure to succeed and provide Susan with the life he promised, Jack urges the rocketry team to take a risk and start testing their experiments at full volume. Sensing the Parsons' mounting frustrations, Ernest invites them to one of his group's secret gatherings, promising a way to make all their dreams come true.
Jack's expert witness testimony at a high profile trial thrusts the rocketry team into the spotlight and helps land them a coveted invitation to The Athenaeum. Meanwhile, Virgil drops off Patty, Susan's rebellious teenage sister, for a disruptive weekend stay, and Ernest's wife, Maggie, makes a surprise return. When Jack's evening at The Athenaeum doesn't go as planned, Jack seeks out Ernest to blow off some steam and ends up on a dark detour into the Los Angeles underbelly.
The team finalizes their prototype but, in a role reversal, Richard has confidence in the design while Jack doubts it will work. Jack leaves the team to test fire without him as he and Susan accept Ernest and Maggie's invitation to go camping in Joshua Tree. While Susan gets better acquainted with Maggie, Ernest uses a mind-bending elixir to teach Jack about the power of Thelema.
A secret return visit to the Agape Lodge leaves Jack wanting more, inspiring him to explore new sexual boundaries at home with Susan, despite her misgivings. Ernest's sudden presence at the Rocketry Team's new desert testing facility has Richard questioning the whole endeavor, until he meets a mysterious woman who helps restore his faith. Meanwhile, Maggie has doubts about Ernest's fidelity.
While Richard and the rocketry team abandon the Suicide Club for more conventional pursuits, Jack delves deeper into the world of Thelema and Sex Magick as a means to convince General Braxton that reaching the moon isn't just comic book fantasy. Susan's concerns about Jack grow after she researches Aleister Crowley and confronts Maggie with the mysterious truths behind this cult religion. Susan's questions leave Maggie at a breaking point, forcing Ernest to confront his inner demons.
Richard flies solo to Washington D.C. to present the team's proposal at the Department of War. But without Jack there to do the talking, Richard must turn to his relationship with Marisol to find the confidence he needs. Back in Los Angeles, Jack continues to drift away from Susan and closer to Thelma, skipping work to go on a spontaneous road trip with a troubled Ernest. Meanwhile, Susan searches for answers behind Jack's behavior by confronting Jack's mother Ruth and the potential source of all Jack's troubles, the Grand Magus himself.
Susan realizes Thelema might be the key to understanding her own psychological wounds. She attends the Agape Lodge for purge sessions with the Grand Magus, while Jack becomes increasingly disenchanted with the religion that promised so much yet delivered so little. Richard and the Suicide Club hit a massive stumbling block, forcing Richard to invite Jack and Susan out to a lavish dinner in an attempt to gain Jack's help. But Jack has been offered a promotion at Pueblo Powder and must decide between providing Susan with the life she always wanted or burying the hatchet...
When Jack receives a letter from Aleister Crowley, inviting him to ascend to the next degree, the Parsons must decide if Thelema is what they both want for their future. After uncovering the truth about Virgil during her purge sessions, Susan is forced to deal with the chilling revelation back in the real world. Richard and Jack finally find common ground, rallying the Suicide Club for a dangerous final demonstration to the military. For the demo, Jack has all he needs except for one crucial element: Ernest.