The returned primarch Roboute Guilliman strives to save the Imperium from an era of death and darkness.

Fell times have come to the galaxy. Cadia has fallen, destroyed by the onslaught of Chaos. A Great Rift in the warp has opened and from its depths have spewed daemons and the horrors of Old Night. But all hope is not lost... A hero, long absent, has returned and with him comes the wrath of the Ultramarines reborn. Roboute Guilliman, the last of the loyal primarchs, has arisen from millennia in stasis to lead the Imperium out of darkness on a crusade the likes of which has not been seen since the fabled days of the Emperor. But never before have the forces of Ruin amassed in such numbers, and nowhere is safe from despoliation. From the dreaded Scourge Stars come the hordes of the Plaguefather, Lord Nurgle, and their pustulent eye is fixed on the Ultramarines home world of Macragge. As the Indomitas Crusade draws to an end, Guilliman and his army of Primaris Space Marines race to Ultramar and a confrontation with the Death Guard.