Horus sends the Worldbearer space marines to the planet Calth, where they are to ambush the loyalist Ultramarines.  In addition to the main fleet, Horus sends a new doomsday battleship for use againsy the Ultramarines home world of Ultramar.  A small strike force travels space and the warp to delay or destroy the doomsday ship to save the Ultramarines.

Horus sends the Worldbearer space marines to the planet Calth, where they are to ambush the loyalist Ultramarines.  In addition to the main fleet, Horus sends a new doomsday battleship for use againsy the Ultramarines home world of Ultramar.  A small strike force travels space and the warp to delay or destroy the doomsday ship to save the Ultramarines.