The new edition of Warhammer 40,000 shifts the narrative lens far away from the Arks of Omen and towards the galactic west, where the true immensity of Hive Fleet Leviathan is revealed. The people of the fortress world Regium are plagued by nightmares of ravenous creatures that Lieutenant Castamon of the Ultramarines 1st Company recognises as the signs of an impending Tyranid invasion, though even he has no idea of the scale of the oncoming catastrophe.