The ForeRunners - Book one - The Sphere

The ForeRunners, humans who left to escape destruction at the hands of the aliens, who just wanted to have fun, as they saw it. Five thousands years later, a sphere left by them on the moon, activates and selects a modern day human ex- soldier to take up the cudgel and save humanity as the aliens return. Three human ForeRunners, all that's left of a once great race,alone on a far distant planet, now try to survive and somehow destroy the destroyers. Getting together has never been so much trouble.