Four modern day teens must figure out a puzzle spanning centuries as they travel through time to save the world from a coterie of evil scientists. Tim is a shy history nerd, Julie is popular and smart, Billy is athletic and confident, and Rose is clever and quirky. But what none of them understand is why Steven Hopkins, a Time Traveler from the 24th century, has chosen them to take on the Emperors of Time. The four teens must travel back to 1916 San Francisco to stop the past from being changed. If they fail, the self-proclaimed Emperors of Time will control the future. Their adventure takes them from a bridge over the Susquehanna River in the days before the Battle of Gettysburg to a settlement of outcasts from the Emperors' futuristic paradise and from the seediest to the swankiest parts of 1916 San Francisco. American History plays as the backdrop for this YA Time-Travel novel.

Tim, the geek, Julie, the popular girl, Rose the quirky one, and Billy the athlete thwarted the Emperors once. But now, the Emperors have a new plan, going back to 1854 to avert the Civil War and set the stage for a future the evil Emperors of Time can control. The four teens must disguise themselves as people who lived in that time to travel back and hopefully frustrate the Emperors' plans once again.

Julie, Tim, Rose, and Billy must now travel back to the Revolutionary War to stop the Emperors of Time from helping the British to win. The teens travel to the past and more than one version of the future while they try to stop the Emperors from controlling the future and our present. Along the way, they find out something strange about Julie's future.