W. Blake Heitzman

Marines from the Nirvanian cruiser, Quantum, board a slave ship to find that the captives committed mass suicide just minutes before their rescuers could free them. Quantum's crew also learns that two escape pods were launched to Earth. One carried an alien predator. Before any action can be taken, Quantum is sent to rescue survivors of a surprise attack on one of their colonies. Earth's fate is now in the hands of its resident aliens.
Alien assisted time travel and history intervention. This book is not sold at Amazon.