Hive Fleet Leviathan bears down on the Octarius sector's heart, while the critical forge world of Sigma-Ulstari fights for its life against repeated xenos invasions. As battles become desperate and the fate of billions hangs in the balance, forces on all sides marshal their deadliest weapons in preparation for the Octarian War's apocalyptic conclusion. From the ashes of Octarius a victor will emerge, tempered in the bloodiest conflict seen in millennia, but who will it be? The Tyranids pit their finest strategic mind, the Swarmlord, against the uncompromising brutality of the Overfiend of Octarius, all while Imperial systems battle to contain the overflowing carnage. You will need a copy of the Warhammer 40,000 Core Book to use the contents of this book.