The Button Man by Davidson King

A visit from Button Man means only one thing: someone wants you dead.

Duke is born into the world a hired killer. It’s his birthright—all he knows, all he thinks he’ll ever be. Then one fateful night, the unthinkable occurs and in the most tragic of moments, a promise is made. That promise is kept for almost fifteen years, until he comes face-to-face with a target he never expects and a future he never sees coming.
Kelly spends his days in a classroom, while his nights couldn’t be more different. Unbeknownst to those around him, their friendly neighborhood teacher is the handler for a hit man. For over a decade he has watched Button Man’s back from behind a computer screen. He is content living his double life, believing he will never cross paths with the dangerous assassin, but fate has a different plan.
When the past collides with the present, Duke and Kelly must prevent it from destroying the future. It’s not just their lives they need to think about—the entire world of a fourteen-year-old girl is about to spin on its axis. Dodging bullets and uncovering truths bring the two closer than they could have imagined. But lust takes a back seat to survival when enemies threaten to drown them both in blood. Can they navigate these twists and turns when death is lingering at every corner, or will they die trying?