Four hundred years ago, an alien race called the Aletheans identified twelve planets in the galaxy that were similar to their own. They sent a survey vessel to each "candidate", hoping to make contact with their inhabitants.

One of the candidates was Earth, but they arrived in humanity's 17th century and soon realised they were too primitive for first contact.

During the mission, an extinction event left their home world desolate and their survey vessels adrift above their subject worlds.

Centuries later, whilst serving in Iraq shortly after the first Gulf War, SAS soldier Ryan Marshall finds himself aboard the vessel dispatched to "Candidate 11".

With the help of a small team of specialists, Marshall must use the alien technology to defend Earth against an imminent destructive force, and harness The Alethean Legacy.