Book 2 in the Warhammer 40,000 Mega-series, "Dawn of Fire".
As the Indomitus Crusade begins, great fleets warships leave Terra on a
desperate mission to stabilise Imperium Sanctus in the wake of the Great
Rift. The returned primarch, Roboute Guilliman, leads a huge force
towards the shrine world of Gathalamor, whose stable warp routes will
allow the flotilla to spread across the beleaguered southern half of the
Imperium.
But grave tidings reach the Imperial Regent's ears. Warnings from an
ancient race and eerie silence from the army tasked with holding the
crucial world until his arrival, lead Guilliman to send a vital mission
to Gathalamor; at its head, Shield-Captain Achallor of the Adeptus
Custodes.
Achallor discovers a world on the brink, a beaten Imperial force and
sinister agents of Abaddon the Despoiler who have unearthed an ancient
evil, a weapon that when harnessed not only threatens the primarch, but
perhaps the holy Throne of Terra itself...