Peyote Trip works in the Deals Department on the Fifth Floor of Hell, where employees travel to any point in human history via tablets, freeze time, and persuade desperate humans to sign contracts trading their souls for granted wishes. Hell is not fire and brimstone but an eternity of petty agitation: bad music, rubbery food, and discomfort repeated forever.
Peyote has spent millennia working toward a single goal: securing soul deals from five generations of one family, the Harrisons. He has completed four and needs only a fifth. A bunkmate named Slippery Pete once shared a secret: if a Fifth Floor employee completes a set from their own direct descendants, they earn a second life on Earth. Peyote's true surname is Harrison.
The Harrisons consist of Silas; his wife, Lily; and their two children, Sean and fourteen-year-old Mickey. Silas's father, Evan, built the family's lake house in New Hampshire, and each summer they return to it. The house carries the weight of a tragedy: Silas's older brother, Philip, was convicted of killing a girl named Sarah Kelly at a party there when the brothers were teenagers. Philip hanged himself in prison three weeks into his sentence. The family also harbors a legend about a supernatural deal-maker who can be summoned in desperate times.
Lily is secretly having an affair with a man named Gavin. Meanwhile, Mickey, who hates soccer but plays because her parents insist, meets Ruth Caroway at practice, a girl a year older who is confident and magnetic. Ruth defends Mickey from a bully, and the two become inseparable. Silas invites Ruth to join the family's six-week summer trip. Lily objects, anxious about what the lake house will stir up.
In Hell, Peyote gains an ally when Calamity Ganon, called Cal, transfers to the Fifth Floor. She presents herself as timid but later reveals this was a calculated act, proposing an alliance with Peyote to undermine their colleague Trey. They discredit Trey to their boss, KQ, the department's domineering manager. KQ assigns Peyote to mentor Cal, giving him access to the Sixth Floor, which houses the Looking Glass, a device that can locate any lost person, object, or memory from human history. Peyote accepts because the Looking Glass is essential to recovering his own lost past-life memories.
Cal's personnel file reveals her backstory: she was raised in a barracks compound in New Mexico by a man called the General, who recruited vulnerable children and trained them as soldiers for a fabricated holy war. The General taught his soldiers never to drink water in Hell, claiming it was the river Lethe and would erase their memories. He branded dead soldiers with a heated key, telling them the mark would identify them as Heaven's warriors. After the barracks were raided, Cal searched for the General's promised paradise, a place called the Farm. When she found it and learned no one there knew her father, she threw a grenade into its schoolhouse. She was killed by police at twenty-six.
At the lake house, old wounds fester beneath the summer warmth. Silas notices that Ruth strongly resembles Sarah Kelly. Lily leaves poppies at the clearing where Sarah died, harboring a doubt she has never voiced: when she woke the night of Sarah's death, Silas had not been in bed beside her.
Mickey, desperate to hold Ruth's attention, tells her the family secret about Philip and Sarah. Ruth proposes a séance to contact Sarah's spirit. Silas discovers the children holding it and erupts in fury. Ruth's influence over Mickey deepens in troubling ways: she shows Mickey how she cuts herself with a blade, framing it as a way to feel grounded, and offers the blade to Mickey. The secret cutting becomes a bond between them. Mickey later sneaks into Ruth's Altoids tin looking for the blade and notices the pills inside are missing.
In Hell, Peyote and Cal secure access to the Looking Glass, but once inside, Peyote secretly searches for his own memories. He prints his results, but Cal's search goes unfinished, and she pockets his printout. Their alliance fractures when Cal sides with Trey and tells KQ that Peyote tried to steal a deal, costing him his Sixth Floor access. Peyote later determines that Cal's true goal is to find the General. He also realizes that Hell's water is the Lethe: Cal's lifelong refusal to drink preserved her memories but caused her body to burn constantly, producing the blisters he noticed when she showered.
The Harrison marriage reaches its breaking point when Silas discovers Lily's affair and asks if the man is Sarah Kelly's brother. Lily asks the question she has suppressed for seventeen years: whether Silas killed Sarah. He denies it, and Lily confesses she is in love with Gavin.
Peyote tracks Cal to a nursing home in Georgia where the General lives. Cal returns his Looking Glass printout, which she always intended to give back. Inside the old man's room, Peyote unlocks the General's cashbox with the key from around his neck, finding film reels of fights among the child soldiers and a ledger proving the General profited from their violence. Cal begins strangling her father, but Peyote pulls her off. Then his tablet beeps: one of the Harrison family members he has been tracking for a deal is disconnecting. He sees Mickey facedown in the lake.
The catastrophe's full scope becomes clear. Gavin Kelly, Sarah's twin brother, orchestrates an elaborate revenge. He seduces Lily to gain access to the family, then sends his own daughter, Ruth, to befriend Mickey. Ruth drugs Mickey with pills from her Altoids tin and leaves her in the lake to drown, mirroring Sarah's death. Gavin ties Lily to the boat lift and confronts Silas in the clearing with a gun and Philip's suicide letter.
The letter reveals the truth buried for seventeen years. Silas, not Philip, was having an affair with Sarah. On the night of the party, Silas struck her and swam back to shore, leaving her drugged and concussed. Philip found her body in the water, attempted CPR, causing the chest bruises the prosecution attributed to murder, and took the blame to protect his brother. He killed himself because he could not live without Sarah.
Peyote and Cal reach the float and revive Mickey. Sean sneaks up behind Ruth and holds a knife to her throat, demanding Gavin drop his gun. Ruth breaks down, confessing she drugged Mickey but could not go through with the full plan because she had come to love the Harrisons. Lily frees herself from the boat lift, retrieves a rifle belonging to Silas's mother, Rose, and shoots Gavin. When he grabs Lily, Ruth strikes him with a rock, killing him.
Silas invokes the family legend and calls out for Peyote, offering his soul for Mickey's life. Peyote understands the cost: completing the set means returning to Earth as his original self, erasing the entire Harrison line from existence, including Mickey. Despite this, he presents the tablet and tells Silas to sign.
In the epilogue, Peyote is reborn on Earth. His Looking Glass printout revealed that in his original life, he traded his soul to save his daughter from cancer. He drives the highways searching for Cal as a child and finds her at twelve, hitchhiking near Shamrock, Texas. He shows her the soda-tab necklace she recognizes from the barracks and invites her into the car, planning to raise her alongside his own daughter. Before his deal is collected, Peyote requests a complete memory wipe so he would not remember Hell, the Harrisons, or Mickey. On Earth, with love restored, he finds that goodness requires only the willingness to try.