Words of Radiance, Part 2 (The Stormlight Archive #2, Part 2) By Brandon Sanderson

Expected by his enemies to die the miserable death of a military slave, Kaladin survived to be given command of the royal bodyguards, a controversial first for a low-status "darkeyes." Now he must protect the king and Dalinar from every common peril as well as the distinctly uncommon threat of the Assassin, all while secretly struggling to master remarkable new powers that are somehow linked to his honorspren, Syl.

The Assassin, Szeth, is active again, murdering rulers all over the world of Roshar, using his baffling powers to thwart every bodyguard and elude all pursuers. Among his prime targets is Highprince Dalinar, widely considered the power behind the Alethi throne. His leading role in the war would seem reason enough, but the Assassin's master has much deeper motives.

Brilliant but troubled Shallan strives along a parallel path. Despite being broken in ways she refuses to acknowledge, she bears a terrible burden: to somehow prevent the return of the legendary Voidbringers and the civilization-ending Desolation that will follow. The secrets she needs can be found at the Shattered Plains, but just arriving there proves more difficult than she could have imagined.

Meanwhile, at the heart of the Shattered Plains, the Parshendi are making an epochal decision. Hard pressed by years of Alethi attacks, their numbers ever shrinking, they are convinced by their war leader, Eshonai, to risk everything on a desperate gamble with the very supernatural forces they once fled. The possible consequences for Parshendi and humans alike, indeed, for Roshar itself, are as dangerous as they are incalculable.