Tombs of Anak (Cooper Kids #3) by Frank Peretti

An angry terror lurks at the bottom of a dark pit...
Jay and Lila Cooper are back for another adventure, this time in search of a young treasure-seeker whose ambitions drove him to the bottom of a pit, never to return. In their struggle to understand what happened to him, the Coopers learn of a greedy, man eating creature known as Ha-Raphah, who terrorizes locals into worshiping him. Although they are certain he is extremely dangerous, Jay and Lila are determined to uncover the truth.

This story of dangerous exploits and a mission to stop an evil that holds a population in its crushing grip will have you hooked from start to finish. Recommended for ages 10 to 14