Gods of Mars (Forges of Mars #3) (Warhammer 40,000)

Beyond the edges of the galaxy, Archmagos Kotov's great voyage is over. He has achieved his goal - to find the resting place of the long-lost Vettius Telok. But Telok yet lives, and as the brave explorators of Kotov's fleet marvel at the wonders laid before them, darker plans unfold. As reality itself is threatened by impossible technologies from the dawn of time, it falls to a small group of heroes to thwart an insane plan that could see the entire universe annihilated.

Read it because

The terrible secret that has haunted the series is revealed, and it sheds new light on the Adeptus Mechanicus's eternal mission to retrieve technology, no matter the cost…