The apocalyptic world depicted in a novel has become reality. And only I know how this novel ends! Kim Dok-ja (Ahn Hyo-seop), an ordinary man in his 20s, is the only reader of an obscure web novel titled “Three Ways to Survive the Apocalypse”. Having started reading in his school days, after 10 years of serialization the novel’s conclusion is finally published, and Kim, not liking the ending, writes an angry letter to the author, calling it “the worst novel”. After sending the letter, the apocalyptic world of the novel suddenly becomes reality, and the novel’s omnipotent hero Yu Jung-hyeok (Lee Min-ho) appears before Kim. As the only person who knows how to survive in this world, Kim and his companions rescue Yu Jung-hyeok and strive to save the world by writing his own, new ending.