Lying in Flames (Legacy of Russ #3)

Daemons rampage across the planets and moons of the Fenris system, and the Space Wolves find themselves hard-pressed to contain the attackers, let alone hunt for their missing Chapter Master, Logan Grimnar. To add to their troubles, a crusade force led by Azrael of the Dark Angels, and backed up by the Inquisition, hangs in judgment above Midgardia. The Space Wolves stand accused of harbouring mutants among their ranks – a terrible crime in the eyes of the Imperium.

Read it because
Daemons on one side, (Dark) Angels on the other – the Space Wolves face their darkest hour.