This fourth sequel to the Book in the Loft addresses the many questions of time travel―whether one can travel to the past or the future without becoming entangled in paradoxes. Neil and Elena MacBruce and the crew of Explorer, along with Surion Captain Torn, find themselves in a predicament that forces them to not only answer the questions, but to experience them. Time travelers from the future invade the Surions' world and take what is not theirs. Explorer's Captain Jon Varkon decides to find the means to track them down, but the current technology within the Inner and Outer Circle of Planets is of no help. Enlisting the aid of the Dropa and an alien race of time travelers called "Torellians," he and his crew set out to retake what was stolen, not sure if they will succeed in their mission or be caught and lost in one or more of time's paradoxes.