Finding the Troll's Heart. Trollkin Lovers, #6

Six months ago, Simka's sister was stolen by wild orcs. When the neutral city of Morgenzan refuses to help, Simka goes on a rescue mission-but she can't find the orc camp alone. Corporal Jar'kel, a grouchy old troll with a broken tusk, has been sent to the frigid Blue Crags to help defend a valuable mine against the wild orcs. When he catches Simka vandalizing the mine, he makes her a deal: if she helps him find the wild orcs, he'll help save her sister, and he can at last return home.
While Jar'kel and Simka work together to locate the camp, Jar'kel denies his growing attraction to the younger human woman. But to succeed in their mission, they must pretend to be a mated pair. Can they keep up the ruse when it feels much too real?