Lords of Mars (Forges of Mars #2) (Warhammer 40,000)

Pursued by vengeful eldar, Magos Kotov’s Explorator armada heads into a newly revealed area of space in pursuit of ancient secrets. As the Adeptus Mechanicus forces and Black Templars Space Marines tackle the twin threats of the wrathful aliens and insurrection aboard the fleet, a greater danger reveals itself...

Read it because

It's a dramatic continuation of the tale from 'Priests of Mars', exploring science fiction ideas and human conflicts within the framework of a Warhammer 40,000 action-adventure drama.