Prospero Burns: The Wolves Unleashed (The Horus Heresy) by Dan Abnett

The Emperor is enraged. Primarch Magnus the Red, of the Thousand Sons Legion, has made a catastrophic mistake that endangers the safety of Terra. With no other choice, the Emperor charges Leman Russ, Primarch of the Space Wolves, with the apprehension of his brother from the Thousand Sons home world of Prospero. This planet of sorcerers will not be easy to overcome, but Russ and his Space Wolves are not easily deterred. With wrath in his heart, Russ is determined to bring Magnus to justice and cause the fall of Prospero.