Susan and Patty's relationship reaches a breaking point when Susan learns of her sister's indiscretions - nevertheless, they must join forces to use Virgil as a means to an end. After Marisol receives devastating news, she gains a new perspective on her relationship with Richard. Jack has a chance to get back into the military's good graces, but the conditions may be too tough to swallow. Yet with the Magus in jail, Jack's power within the Agape rises to new heights; however, the arrival of a new prospective tenant at the Parsonage threatens to change all that. Season finale.

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.

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.

Following the disastrous party at the Parsonage, Jack loses his security clearance and must strike a dangerous bargain with Wallace to be reinstated. With the police now investigating the Agape, the members' deepest secrets are revealed through a shocking betrayal. Meanwhile, Richard, Chiang and Mesulam are sent to London for a military research project, where Richard goes to great lengths to clear Jack's name. Devastating truths come to light, putting Jack and Susan's future in doubt, and creating the opening that Patty has been looking for.

After Professor Mesulam gives his blessing to the project, Jack and Richard set off to create Caltech's first ever rocketry team. But Caltech's acceptance has come with caveats, and, coupled with Ernest's looming presence, Jack and Susan are feeling more on edge than ever before, desperate to figure out whether Ernest's intentions are evil or not.

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 Magus invites Ernest to stay at the Parsonage, leading Jack to question both men's motives. Richard discovers that Marisol has been hiding a secret from him that could jeopardize their relationship. In an effort to join the ranks of the Agape, Patty shares a shocking discovery with Jack. And with the new rocketry project already on the ropes, Jack finds help from an unlikely source, Aleister Crowley himself.

Jack's breakthrough fuel formula goes missing from his office, and Jack suspects it was stolen by an enemy spy. As he seeks out Ernest's help to deal with the situation, Susan seeks out the help of the Magus as she attempts to mollify their conservative, upper crust neighbors. When Virgil learns that Patty has also joined the Agape, he turns the screws on Ernest, forcing the broken zealot to choose between loyalty to his beliefs or facing a life behind bars.

Jack's conjuring of the Angel earns Ernest's loyalty but divides the Agape, spurring the Magus to investigate the so-called 'miracle.' Marisol attempts to confront her father about the secret that destroyed their family as Richard deals with his broken heart by diving deeper into the rocketry project. Meanwhile, when Susan's attempt to get Thelema officially recognized as a religion hits a roadblock, she turns to Ernest in hopes of putting a stop to Virgil's harassment once and for all.

Jack sees his ambitions threatened as Agent Wallace grows increasingly suspicious of Jack's ties to Aleister Crowley. In an attempt to clear the air, Jack invites Wallace, General Braxton, and their military colleagues to the Parsonage for a summer dinner party - hoping to show them they have nothing to fear - but his best laid plans go awry as dark secrets are revealed and Ernest takes drastic steps to achieve transcendence.

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.

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.

The U.S. Military offers Jack, Richard and the Aerojet team a classified mission that could turn the tide of World War II, but which comes with increased scrutiny of Jack's personal life. As Jack strives to straddle the worlds of mysticism and science, Virgil Byrne's crusade against the Agape Lodge forces Jack and Susan to offer the cult safe haven in their Pasadena mansion, only to have their lives further disrupted by the return of Ernest Donovan, who has come back to Los Angeles more broken than ever.

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.

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.

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 with Richard to continue their rocketry dream.

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.