On his last day as a contract office worker at Minosoft, Kim Dok-ja finishes the final chapter of the web novel Three Ways to Survive the Apocalypse (TWSA) and finds the ending unsatisfying. He writes a sharp review to the author, "tls123," before an unexpected prompt arrives: the author urges him to craft a new ending himself. As he heads home on the subway with his colleague, Yoo Sang-ah, the moment shifts from routine to surreal when a mysterious message from the writer appears, nudging him toward a reinvention of fate.
At 7:00 p.m., the train comes to a sudden stop and a dokkaebi named Bi-hyeong materializes, declaring that humanity must endure a series of trials set by constellations. The first trial requires someone to kill one or more living beings. Dok-ja quickly realizes the scenario mirrors the opening of the novel. In a desperate bid to survive, he kills an ant from a boy named Lee Gil-yeong's insect box. His instinct is to help others, but panic spreads and blood is shed. When the test ends, only Dok-ja, Sang-ah, Gil-yeong, and fourteen others remain, and they are all asked to choose a sponsor. Dok-ja refuses.
The train is then attacked by a monstrous creature, forcing the group to flee. A soldier named Lee Hyeon-seong, a comrade from Joong-hyuk’s world in the novel, lends a hand and helps them escape. Dok-ja spies Yoo Joong-hyuk in the midst of a fight and proposes an alliance to alter his own fate, knowing Joong-hyuk will fall in battle against the Fire Dragon. Joong-hyuk rejects the alliance, pushing Dok-ja off a bridge, and the latter is swallowed by an ichthyosaur. Inside the creature, Dok-ja strikes a deal with Bi-hyeong to earn coins and uses thorny goods from the dokkaebi shop to slay the beast. He trades its nucleus for a rare item, the Ether of Faith.
After a stop at a convenience store, Dok-ja rescues Jeong Hui-won, a minor character who would have perished in the novel, and they escape another monster. The group regroups at Geumho Station with Sang-ah, Hyeon-seong, and Gil-yeong. Here the scenario shifts: kill all monsters or pay a daily coin fee to survive. Congressman In-ho becomes a looming menace, urging Dok-ja to share his coins, but Dok-ja sees through his deception. Joined by Hui-won, the survivors learn that In-ho and his men have been exploiting the coins to prey on others. When Sang-ah is kidnapped by a Ground Rat, Dok-ja defeats it with White Star Pure Energy and rescues her and Hyeon-seong, who had been trapped in an Illusory Prison born from a trauma of witnessing a comrade’s death by grenade.
New weapons arrive for the group, including Dok-ja’s broken sword, named "Broken Faith," which must be fused with the Ether of Faith to become whole. His vast knowledge of the novel raises suspicions, so he fabricates a lie about prophetic powers and claims the key to their survival lies in preventing Joong-hyuk’s death at Chungmu-ro. Their next obstacle targets the Geumho monster, ultimately revealed to be In-ho himself, who has become monstrous by surrendering his humanity to the constellations. He is thwarted when Lee Ji-hye intervenes at the last moment and kills In-ho, saving Dok-ja’s group.
Arriving at Chungmu-ro, the survivors face a tense round where only green zones can ensure safety; others will be killed. Dok-ja discovers a hidden bonus zone and, choosing solidarity over self-preservation, gives it to Gil-yeong and declines Joong-hyuk’s demand to sacrifice the boy. He also consumes a crystal from the Ground Rat and is dragged into the Illusory Prison, where a painful high school memory resurfaces: he was forced by bullies to fight his best friend, Ahn Min-seop, to win and avoid bullying, an act that indirectly drove Min-seop to suicide. He had once told tls123 that he hoped for an ending where the protagonist survives with his companions. Joong-hyuk, speaking through a Dream Conversation, challenges that idealism, explaining that his past belief in cooperation was crushed by the harsher reality of human nature.
When Dok-ja awakens, he realizes his teammates protected him and endured without the green zones. He resolves that they can endure together and decides to confront the Fire Dragon without sacrificing Joong-hyuk. With only one green zone left for Gong Pil-du, a man with the most coins, Dok-ja offers to buy it. [Lee Ji-hye] initially refuses to help, but breaks down after Dok-ja confronts her about the murder of her best friend in the opening scenario. With 113,000 coins, Dok-ja buys and, with Ji-hye’s help, destroys Pil-du’s green zone, urging everyone to survive as a unit and also pays Pil-du 100,000 coins to safeguard the others.
Pil-du is moved by the act and agrees to fight alongside them. When the Fire Dragon finally emerges, the team attempts a coordinated strike: Dok-ja would break the shell, Sang-ah would hold the beast, and Hui-won would pierce the core to earn the “King of No Killing” ability that could revive Dok-ja if the shell-breaking proved fatal. The plan is interrupted when Joong-hyuk dies before the revival can take effect. As the world begins to crumble, Joong-hyuk receives a notification that his ichthyosaur nucleus has been traded for the Ether of Faith, a deal initiated by tls123, the author.
Dok-ja then fuses the Ether of Faith with Broken Faith to forge an Attribute Weapon, defeating the Fire Dragon and reviving Joong-hyuk with the King of No Killing, thereby saving the world. Joong-hyuk expresses gratitude, and the surviving group celebrates their narrow victory. Dok-ja declares his intention to write a new ending together with his comrades, ensuring a future where they can stand united.
In a mid-credits scene, Han Myeong-oh, the former superior of Dok-ja, arrives to reveal that Geumho has been destroyed and that all the other survivors are dead except for him. A distant train sound hints at another looming scenario, leaving the door open for what comes next.
