Jason Dessen is the protagonist. He was born in 1973 in Denison, Iowa and has a brother, Michael, with whom he is not close. Jason’s mother died of pneumonia due to an underlying heart condition; this imprinted a strong fear of losing his loved ones to disease. At the beginning of the novel, Jason is 42 and lives in a brownstone in the Logan Square neighborhood of Chicago with his wife of 15 years, Daniela, and their 14-year-old son, Charlie. Jason teaches quantum physics at Lakemont College. He envies his friend, Ryan Holder, who became a famous, award-winning scientist. Jason chose to give up his career as a research scientist when Charlie was born, as Charlie suffered serious medical issues and Daniela suffered from severe postpartum depression. While caring for his family, Jason lost his funding and his position. Though he loves his family and he's relatively happy, Jason often wonders what his life would have been like if he'd continued with his career instead.

After Jason’s abduction and during his nightmarish experiences trying to get back to his own world, he comes to realize his life with Daniela and Charlie is the one he wants. He rejects Jason2’s life as a ruthless, groundbreaking scientist, and he sees that in other worlds, even when he decided not to marry Daniela, his choices did not lead him to a prestigious scientific career.