for The Traitor's Game by Jennifer A. Nielsen
Kestra Dallisor has spent three years in exile in the Lava Fields, but that won't stop her from being drawn back into her father's palace politics. He's second-in-command to the cruel king, Lord Endrick, which makes Kestra a valuable bargaining chip. A group of rebels knows this -- and they snatch Kestra from her carriage as she reluctantly travels home.
The kidnappers want her to retrieve the lost Olden Blade, the only object that can destroy the king, but Kestra is not the obedient captive they expected. One of the rebels, Simon, has his hands full as Kestra tries to foil their plot, by any means necessary. As motives shift and secrets emerge, both have to decide what -- and who -- it is they're fighting for.