Dark Apostle (Warhammer 40,000 Novels: Chaos Space Marines)

Driven on by dark visions, Dark Apostle Jarulek of the Word Bearers and his force lay waste to the Imperial planet of Tanakreg. After brutally enslaving the population, they set them to work building a monstrous, kilometres-high tower. What is the Word Bearers' vile purpose, and can they achieve it before the Imperial forces arrive to reclaim the planet?