A Mutiny in Time - James Dashner

Time travel is real... and it's our only hope! When best friends Dak and Sera are recruited by the secret society of Hystorians, they learn that nothing in their world is as it should be. Now it's up to them and their new ally, Riq, to visit the past and fix the Great Breaks in history. Their first stop: Spain, 1492, where a sailor named Christopher Columbus is about to be thrown overboard in a deadly mutiny.