As the war in the Damocles Gulf continues to rage between the Imperium and the Tau Empire, the alien-hunting Deathwatch discover the existence of an enemy weapon that could tip the balance of the conflict against them. The deadly Stormsurge is the apex of alien tau technology, capable of destroying even the mighty Titans of the Imperium. Though the Deathwatch have located the threat, they alone cannot vanquish it and one of their number must call upon his erstwhile brothers in the White Scars Chapter for aid, an alliance that will stretch the bonds of brotherhood to their very limit.