The beauty of destruction

In the far future, after the Loss of Earth, war has begun and an unknowable alien race has awakened, intent on the destruction of everything. Here and now, the end of the world has come. And the only way our species will survive is if two augmented humans can fight their way through apocalypse to a faint glimmer of hope. Long ago, the seeds of that apocalypse were resisted by the warrior tribes of Britain, with devastating consequences for them and their lands. And all three of these times will meet on another world . . .