The Saints of Salvation: Peter Hamilton

Humanity welcomed the Olyix and their utopian technology. But mankind was tricked. Now these visitors are extracting a terrible price.
For two years, the Olyix have laid siege to Earth, harvesting its people for their god. One by one, cities are falling to their devastating weaponry. And while millions have fled to seek refuge in space, others continue to fight an apparently unwinnable war.
As Earth's defeat draws near, a team attempts to infiltrate the Salvation of Life - the Olyix's arkship. If it succeeds, those chosen will travel to a hidden enclave thousands of light years away. Once there, they must signal its location to future generations, to bring the battle to the enemy. Maybe allies scattered throughout space and time can join forces. Yet in the far future, humanity are still hunted by their ancient adversary. And as forces battle on in the cold reaches of space, hope seems distant indeed…