On December 12, a group calling themselves the Elite upload an article to various websites, saying that The End Is Nigh and that the sinners will start to die on December 13, with the number of deaths doubling each day. Most people don't take it seriously, until several high-profile criminals suddenly suffer violent convulsions and die. Meanwhile, Olympia Dorsey, a single mother raising her thirteen-year-old daughter Nicki and her eight-year-old autistic son Hannibal, and their neighbor Terry Nicolas, an ex-Special Forces soldier, visit Golden Dream, a martial arts studio run by an international religious movement, where the instructors believe that Hannibal has incredible untapped potential. The movement's guru, Madame Gupta, invites Olympia and Hannibal to stay at Salvation Sanctuary, a retreat in the mountains, where Hannibal can learn to access his abilities, but she doesn't tell Olympia about the group's secret plans for Hannibal.
Twelve Days contains examples of:
- Auto Erotica: Swedish arms dealer Thor Swenson is driving while being given a blowjob by his assistant when the convulsions strike.
- Big Guy Rodeo: During a demonstration at the dojo, Madame Gupta fights with Terry, and effortlessly beats him. At one point she vaults between his legs and leaps onto his back.
- Couldn't Find a Pen: A waitress who flirts with Terry leaves her number on his napkin in pink lipstick.
- Disappeared Dad: Olympia's husband Raoul left three years ago because he couldn't handle Hannibal's autism. Olympia hasn't heard from him in eighteen months. Hannibal has been told that his father is dead.
- Enlightenment Superpowers: Through meditation, Madame Gupta has gained Super-Strength, the ability to move in just the right way to effortlessly win every fight, and the ability to catch glimpses of the history of people and places. With Gupta's help, Terry gains similar abilities, although he isn't as powerful as she is.
- Eyes Always Averted: Hannibal has been avoiding eye contact since he was eleven months old.
- Faint in Shock: On December 14, the ex-governor and drug lord Ramone Quinones dies during a televised interview. The interviewer faints.
- Happy Place: Hannibal imagines himself in "the Game," a giant house that doubles as a Memory Palace. Each wing has ten stories, each story has ten corridors, each corridor has ten rooms, each room contains ten objects, and each object has ten hooks, on which his memories are hung. Hannibal loves being in the Game, where he's safe and alone, but never bored. In the real world, he spends most of his time attempting to draw the house, then either erasing it or crossing it out when he's done.
- It's All My Fault: An elderly widow with terminal cancer wonders if the impending apocalypse is her fault, because she prayed to God to not let her die alone. She thinks God misunderstood and decided to kill the whole world with her.
- Kick the Dog: When goons kidnap Nicki from Olympia's condo, Pax, the Great Dane she's dogsitting, attacks one of them. He tases Pax. Later, as the goons are carrying Nicki out, one of them tases Pax again, even though he's still helpless on the floor. Pax gets his revenge the next day by ripping the goon's throat out.
- Long Last Look: Corwin takes a last look around his room at the Salvation Sanctuary, before his handlers take him to be killed.
- Maligned Mixed Marriage: Madame Gupta's mother was Brahmin, and was disowned by her family for marrying a Siddi man.
- Meet Cute: Olympia and Terry first met last year at a barbecue, when Hannibal ran ahead of Olympia, ran into Terry, and almost bounced off him into an empty swimming pool. Terry caught him. He and Olympia began a short-lived relationship, which she broke off because she was afraid of betrayal.
- Middle Name Basis: Nicki's full name is Eva Nicole Dorsey.
- Military Brat: Terry grew up on a series of army bases with his widower father, moving every few years. When he was fifteen, a tae kwon do instructor in Dallas implanted a kundalini trap, planning to remove it in a few months. But Terry's father moved before he had time, meaning that Terry lived for over two decades with the block until Gupta finally helps him remove it.
- Neurodiversity Is Supernatural: Madame Gupta tells Olympia that Hannibal is an "indigo child" whose disability is caused by a kundalini trap - a blockage of his energy - that she can help him release. She actually wants to use his powers to kill people, because he's the only person she's ever met who's powerful enough to kill people without killing himself. Instead he turns his powers on Madame Gupta and all her accomplices.
- Parent Never Came Back from the Store: When the Dorseys still lived in Miami, Raoul left the house, saying he was going to get pizza and would be back in twenty minutes. Instead of coming home, he emailed Olympia saying he needed to work things out. The next she heard was from his lawyer.
- Parent with New Paramour: Terry is a type 1 for Hannibal, who loved him from the moment they met and is always thrilled to see him, and a type 2 for Nicki, who didn't learn to like him until he proved himself by saving her family from Salvation Sanctuary.
- Spies In a Van: Some spies lurk around Olympia's neighborhood in a cable truck so they can gather information on the inside of her home so they can model her and Hannibal's prison to look as much like it as possible. Olympia thinks one of her neighbors must have been ordering a lot of HBO.
- Sympathetic Magic: Sufficiently powerful people can kill others from across the world by ingesting some of their DNA, meditating on the victim, and then being killed, thanks to quantum entanglement.
- Textual Celebrity Resemblance: Terry is described as looking like the love child of Harry Belafonte and Eartha Kitt.
- Tongue Trauma: Russian arms dealer Fiodor Nabokov bites off his tongue during his fatal convulsions.
- Tropical Epilogue: Terry, Olympia, Nicki, Hannibal, and Pax all move to the isolated Mexican village of Santa Tia. Months later, they're joined by Terry's friends, who are now multimillionaires from selling the Salvation Sanctuary's rare books. Mark offers Terry his cut of the money, but Terry refuses, saying he only wants to be with his family.
- Water Torture: Olympia's kidnappers waterboard her after her first escape attempt. They threaten to do it to Hannibal if she doesn't behave.
