The Vivero Letter by Desmond Bagley

A search for treasure in a lost Mayan city becomes a fight for survival against a band of uncompromising murderous mercenaries…

Jeremy Wheale's well-ordered life is blasted apart when his brother is murdered by a small-time American crook. The killer was after a family heirloom - an antique gold tray - and to find out why his brother died, Wheale follows a trail that leads from Devon to the tropical rainforest of Yucatan.

There he joins the hunt for a fabled hoard of gold - treasure from a lost city of the Mayas. But the jungle hides many secrets, and in its dense cover his brother's enemies are only waiting their chance to strike at Wheale. And with them are a band of vicious convict mercenaries…