Dark Matter

Jason Dessen is a physics professor at Lakemont College in Chicago, married to Daniela and raising their teenage son Charlie. Years earlier, he chose family life over the research career he once hoped would make him a celebrated physicist. One Thursday night, after visiting his friend Ryan Holder to celebrate Ryan's Pavia Prize, Jason is abducted by a man wearing a geisha mask. The abductor knows intimate details of his life, questions whether he regrets his choices, and drugs him at an abandoned South Chicago power plant. Jason awakens at Velocity Laboratories, where strangers expect him to be a renowned scientist returning from a dangerous experiment. He escapes and finds a different version of his own home: he is unmarried, Charlie does not exist, and records credit him with an award-winning physics breakthrough and leadership at Velocity. Meanwhile, chapters told from Daniela's perspective show a Jason who returned to their family home on the night of the abduction and seems unusually affectionate but increasingly unfamiliar.

Searching for answers, Jason finds an alternate Daniela, now a successful artist, and learns that in this reality he ended their relationship when she became pregnant. Ryan Holder, a neuroscientist in this world, mentions having developed an unexplained compound for Jason and Velocity. After an armed intruder murders the alternate Daniela, Jason is recaptured. Velocity's director, Leighton Vance, shows him an immense sealed quantum box built by the version of Jason who pursued scientific success. Ryan explains that his compound temporarily suppresses brain activity associated with conscious observation. Jason reasons that the drug, combined with the box's isolation from external observers, permits a person to experience a superposition of possible realities. Recalling the abductor's private questions, he concludes that the scientist who built the box crossed into his world and exchanged their lives in order to become Daniela's husband and Charlie's father. This other man is called Jason2. Amanda Lucas, a Velocity psychiatrist disturbed by the laboratory's coercion, helps Jason escape into the box after reporting that Ryan has been killed.

Inside the box, Jason and Amanda perceive a seemingly endless corridor lined with doors opening onto alternate worlds. They do not initially know how to navigate it. Their early experiments lead to a ruined Chicago under falling ash and a world of deadly snow, where they nearly freeze. They later witness another Jason and Amanda attempting to escape a different Velocity laboratory; that Amanda is shot while her companion is incapacitated. The pair begin to suspect that expectations and emotional states influence the destinations available behind the doors, but their theory remains provisional. As their supply of the compound dwindles, they experience an advanced Chicago and a plague-stricken city in which Charlie has died and a gravely ill Daniela says that world's Jason has also died. Jason comforts her and, with her consent, administers medication that ends her suffering. Repeated visits to Chicagos that almost match his own make his search increasingly obsessive. Amanda eventually leaves, arguing that he has been writing the physical details of his home without reckoning with what he feels. Alone, beaten and robbed of most of his remaining supplies, Jason becomes homeless in another reality and briefly considers murdering a counterpart to take his place, but rejects the deception. He makes a final effort to navigate by remembering the emotional experience of first meeting Daniela.

Jason emerges in a Chicago whose personal details match his own, only to discover that many other versions of himself have independently returned there after diverging during their journeys through the box. They share his memories of Daniela and Charlie and compete for the one family life Jason2 stole. A private online chat reveals that some have armed themselves or contemplated killing their counterparts. Jason narrowly escapes attacks by other Jasons and realizes he cannot predict their moves because they think much as he does. He deliberately provokes his own arrest at a diner to get Daniela to come to a police station without approaching their watched house. When she arrives, he proves the man living with her is an impostor by calling his Lakemont office and having Daniela test that man's false memory of a family trip. They collect Charlie from school and move to a crowded mall, where Jason explains the abduction, the quantum box, and the competing versions of himself. Daniela and Charlie choose to trust and accompany him, though Daniela understands that other Jasons may love them just as sincerely.

The family flees to a remote Wisconsin cabin. Hoping to avoid further bloodshed, Jason proposes an online lottery among the returned Jasons to determine who will remain with Daniela and Charlie, but many reject the proposal, and Daniela refuses to be treated as a prize. She tells Jason that their particular shared history makes him irreplaceable. Their refuge is then discovered. One violent counterpart attacks Jason and tries to take his identity; Jason2 arrives and kills that attacker, then threatens Jason. Daniela confronts Jason2 about the damage caused by his attempt to undo regret. When Charlie distracts Jason2, Jason stabs him and retrieves the keys to their Suburban and his stolen wedding ring. Jason2 remains alive when they depart. The family survives further gunfire and escapes, but Jason concludes that a lottery cannot protect them. He learns that Jason2 left a bag of the compound in their vehicle.

With no safe future in their own Chicago, Jason, Daniela, and Charlie return to the abandoned power plant. Approximately fifty other Jasons have assembled for the proposed lottery. Daniela insists that she and Charlie will enter the box with the Jason they chose. Although some object, another counterpart argues that her wishes and Charlie's needs should govern the decision, and the others let them through. Jason gives each family member the drug, and they walk the corridor together. To make their next destination less predictable to the other Jasons, the parents entrust the choice of door to Charlie. He opens it onto brilliant light and the scent of wet earth and unfamiliar flowers after a storm. The novel ends with the family together at the open doorway, without identifying the new world or showing what happens to them there.