Wraithflight (Black Library Advent Calendar 2014 #4)

As Hive Fleet Leviathan spreads across the galaxy, the eldar of Iyanden enact a desperate plan to stop a splinter of the fleet that could spell doom for the already-ravaged craftworld. Iyanna Arienal leads an armada of sinister wraithfighters and other deadly spacecraft to aid a human fleet in battling the tyranids - but her true motives may be far more sinister. Read it because
Buckle up and prepare for supersonic combat as the wraith fighters of Iyanden take on a tyranid horde. This tale follows on from Guy Haley's Valedor novel, not essential reading beforehand, but awesome if you have.