The Accelerators #1

Time travelers, Alexa and Bertram, pursue each other through the decades in a deadly chase. Each is armed with a time machine that has one rule: it can only move forward in time, never backward. Alexa must leap further into the future, with Bertram never far behind. Caught in the crossfire is Spatz, a teenager from the 1990s who tries to help but instead gets dragged into another time.