Stalking Darkness: Book Two of the Nightrunner Series by Lynn Flewelling
Seregil's friend and Mentor, the wizard Nysander, has long been the guardian of a deadly secret. In a secret, silver-lined room hidden well beneath the Oreska, he has served for most of his 300 years as the keeper of a nondescript clay cup. But this cup, combined with a crystal crown and some wooden disks, forms the Helm of Seriamaius, and any mortal donning the reconstructed Helm will become the incarnation of the god on earth.
Nysander holds the cup and Mardus the wooden disks--one of which was responsible for Seregil's coma--but the crown must still be located. Threatened under pain of death by Nysander to keep his quest a secret even from his loyal companion, Alec, Seregil is dispatched to find the last missing piece of the Helm so that he and Nysander can destroy it. But this is only the beginning of one of his deadliest journeys ever, for the prophecy also holds that four will come together in a time of darkness, and gradually all that Seregil values is placed at risk as he, Alec, Nysander and Micum are drawn into a deadly web of terror and intrigue.