The final book in the Mephiston trilogy...but how does it end?

Having fought during the devastation of Baal, Mephiston and a cohort of Blood Angels are drawn by cryptic visions to a wartorn world on the cusp of the Great Rift. Here, the sorcerers of the Thousand Sons seek to unite nine Silver Towers and bring about a ritual that will empower their master, the daemonprimarch Magnus. The ritual must be prevented, lest the entire subsector be cast into Chaos. Mephiston faces a challenge like no other, of his strength and his will, confronting a hidden truth that threatens to expose him to his darkest fears.