The Infinity Ring Series
by Various Authors
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.