Assassin's Blade (Throne of Glass #.5)

Celaena Sardothien, one of the most feared killers across the continent has been sent on a mission to Skull's Bay with her archenemy Sam Cortland. But when they discover they have been led by deception, the time will come for the team to go against the orders of their master.

Assassin's Blade is book number .5 in the Throne of Glass series by Sarah J. Maas