Shadow Captain (Space Marine Battles Novella)

On Lepidus Prime, the beleaguered Space Marines have an unlikely ally – the eldar of Craftworld Saim-Hann. With these ancient enemies of mankind engaging the ork invaders, Shadow Captain Krevaan of the Raven Guard sees a chance to strike back against the greenskins. Forging a fragile alliance with the eldar, Krevaan prepares to stop the orks before they can despoil the vital city of Reclamation. But the Raven Guard, no strangers to hidden agendas, suspect a sinister motive to the eldar actions...

Read it because
The Raven Guard pick up the baton from the White Scars and continue the war against the Overfiend, and author David Annandale gets to the heart of what makes the sons of Corax tick.