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?
The kids of The Apex raid a musical car before descending on a village of unsuspecting turtles - but before they can complete their mission, leaders Grace and Simon are separated from the pack under mysterious circumstances.
Grace and Simon look on the bright side and hope that this will be like a mini-vacation from their responsibilities as leaders of The Apex.
The gang's uneasy alliance is tested by a challenge in their first car together: dancing in a high-stakes octopus debutante ball!
Stuck in a blizzard, the gang seeks shelter in a nearby cabin. But when Simon realizes who's inside, he frantically searches for a way out.
A giant, color-changing clock creates a shifting-maze puzzle that the gang has to solve before they can leave the car.
The Apex are just a car away! They're almost home! But first they have to make it through a forest full of pinecone camp counselors.
The gang finds themselves in a car full of golden winged snakes, but in that dusty landscape a mystery they're unprepared for awaits them.
In the seemingly innocent Hey Ho Whoa car, a shocking revelation rocks Grace and Simon's world. Will they be able to fix it before The Apex find out?
The gang is finally ready to meet The Apex again, but keeping secrets has consequences.