The Lion's Roar by Michael Rogers (Paperback)

Terran, a young genius abandoned to poverty, feels called to something great. He is given that chance when Naomi and Rictor, intergalactic missionaries of the Bound, arrive at his doorstep. They offer a simple choice, to travel the stars with them or stay behind and fend for himself.

When an attempt is made on his life before he leaves the planet, he starts to question his decision.

Naomi, meanwhile, is in contact with the Bound's enemies, forced to do their bidding while they hold her son captive.

Rictor just wants to keep the ship from falling apart.

As their individual lives begin to unravel, it becomes apparent that all three are tied together, destined to finally put an end to their mutual enemy. Unless the universe collapses first.