I only have very scant information I'm afraid. Set in either Spain or South America. A boy disappears and a girl finds him imprisoned in a hole in the ground. Possibly his own family arranged the kidnapping. Also something about older brothers wounding their younger brother's ankle to stop him running away.
Think I read it in the 1980s. Female author with 3 part name ie like Joyce Carol Oates only not.
I'm not even sure I enjoyed it that much but it's driving me mad!