Traveling through a barren, otherworldly wasteland, the Infinity Train is full of puzzles and perils. For those in mental turmoil, they can climb aboard and suddenly find themselves wandering its length where each car is a whole other world. Each passenger has his or her own story that led them onto the train, but once aboard, the goal is both simple and difficult: by solving the mysteries of the train and interacting with its strange denizens, solve one's own mental troubles and through it hopefully find their way off the train.
13-year-old Tulip finds herself on a mysterious train with an endless number of cars, each one its own universe, and must find a way to get home.
New passengers. New mysteries. What’s in the next train car? Mirror Tulip (M.T.), the mirror version of Tulip first seen in Book One's "The Chrome Car," now wanders the train both to avoid the Mirror Police and to find a purpose. She comes upon a passenger named Jesse who suffers from bullying issues as well as a deer they name Alan Dracula that has mysterious powers.
In Book 3, Grace and Simon are the leaders of the Apex, an anarchic group of kids on a mysterious train. During one of their destructive missions, Grace and Simon get separated from the rest of the Apex and must find their way back. As the duo navigate through the myriad worlds of the train, they meet Hazel, an optimistic young girl, and Tuba, her gentle gorilla companion. Will Grace and Simon find new inspiration in Hazel’s innocence, or will the ways of the Apex recruit yet another aboard the train?
Book 4 will now follow two old friends with dreams of becoming rock stars who find themselves on the Infinity Train. They must explore the locomotive's inner puzzles — and their own relationship — in order to return home, together.