The novel tells the story of a teen named Bob Miller whose scientist father, Sam Miller, has invented a "time ring", a circular device that allows time travel.
Beginning in the Mesozoic Era, Tom's planned destination, the story depicts various adventures while the travelers jump from point to point in Earth's prehistory; although they are able to locate the missing Dr. Tom Miller almost immediately upon arriving in the Mesozoic era, the time machine is unexpectedly damaged when a dinosaur runs into it.
As a result, the three are unable to immediately travel directly forward through time to their present, and instead are forced to "hop" through different eras of prehistory until they finally arrive home.
This book was used in many elementary and middle school classrooms for reading and literature classes,[citation needed] and gained a notable popularity with its straightforward, dramatic writing style.
[citation needed] The book was originally published in hardcover by Westminster Press in May 1966 and in paperback by Scholastic Corporation.