Dead to Rites (Vintage Paperback) by Sylvia Angus

Meet the irrepressible Mrs. Wagstaff, who has been reading mystery stories for years (and usually solving them before the end of the second chapter). Mrs. Wagstaff is with a group of tourists at a hacienda in Mexico, and she knows very well that the nearby Mayan ruins were once the site of ferocious, bloodthirsty rituals.

But she is hardly prepared to discover the corpse of a young, beautiful girl floating in the sacred pool of the virgins…