James Dashner 
Mutiny in Time [EPUB ebook] 

History is broken, and three kids must travel back in time to set it right! When best friends Dak Smyth and Sera Froste stumble upon a 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. First stop: Spain, 1492, where a sailor named Christopher Columbus is about to be thrown overboard in a deadly mutiny.