When best friends Dak Smyth and Sera Froste stumble upon the secret of time travel - a hand-held device known as the Infinity Ring - they're swept up in a centuries-long secret war for the fate of mankind. Recruited by the Hystorians, a secret society that dates back to Aristotle, the kids learn that history has gone disastrously off course. Now it's up to Dak, Sera, and teenage Hystorian-in-training Riq to travel back in time to fix the Great Breaks . . . and to save Dak's missing parents while they're at it.

Dak, Sera, and Riq might be in over their heads when they attempt to stop a Viking invasion! Hundreds of ships carrying thousands of warriors are laying siege to medieval Paris. The Parisians are holding their own, but the stalemate can only last so long. And that's bad news -- especially since Dak has been captured, forced to work alongside the Vikings while Sera and Riq defend Paris from within. No matter which side wins, the kids lose!

Fix the past. Save the future. Dak, Sera, and Riq return to the United States and walk immediately into a deadly trap. The year is 1850, and the nation is divided over the issue of slavery. In these dark days, the Underground Railroad provides a light of hope, helping runaway slaves escape to freedom. But the SQ has taken control of the Underground Railroad from within. Now Dak and Sera are left wondering who to trust... while Riq risks everything to save the life of a young boy.

What is the secret history connecting the SQ to the Ancient Maya? Book includes an all-new Hystorian's Guide - your key to unlocking the fourth episode of the action-packed Infinity Ring game.

Europe is in the grip of the Dark Ages, but there is a light in the dark: Baghdad. The great city has become a center of learning, populated by scholars, merchants, and explorers from all across the known world. But danger lurks in the desert... and Dak, Sera, and Riq must act fast to save the world's greatest library from utter destruction.

World War II is raging across Europe, and the Axis and Allied powers are in a stalemate. Dak, Sera, and Riq can tip the scales in the Allies' favor... if they can pull off the most daring spy mission of all time. But even if they succeed, are they playing into the SQ's hands?

They've sailed on the Santa Maria, defended famous cities from Vikings and Mongols, and come face-to-face with some of the greatest figures in history. Now, at long last, Dak, Sera, and Riq travel back in time to the moment it all began. Their mission: to save the life of young Alexander the Great. But they are not the only time travelers in ancient Greece. An epic battle against their most dangerous foe awaits them . . . and history will be written by the victors.

The New York Times best-selling series returns - and so does Matt de la Peña! Dak, Sera, and Riq have fixed the Great Breaks in history - but the SQ isn't beaten yet, and the biggest, boldest Infinity Ring adventure of all time has just begun!