Hive Fleet Leviathan is spreading across the galaxy, and the Eldar of Iyanden must take on the desperate task of stopping a fragment of this fleet that could finally finish off their already battered artificial world. Iyanna Arienal leads an armada of sinister spectral fighters and other ships to aid the human fleet as it battles the Tyranids. However, Iyanna's true motives are no less sinister.