What is hidden

Summary/Review: "Former navy SEAL Alan Burke is on the trail of a serial killer--and determined to protect Jo Summerlin. As stubborn as she is beautiful, she insists on following a hunch into the limestone caverns snaking beneath Missouri. They both know that they may be descending into a monster's lair. To get Jo out alive, will Alan have to make the ultimate sacrifice?" -- Page [4] of cover.