The Vivero Letter by Desmond Bagley
Action thriller by the classic adventure writer set in South America.
Jeremy Wheale's well-ordered life is blasted apart when his brother is murdered. The killer was after a family heirloom - an antique gold tray - which sets Wheale on a trail from Devon to the tropical rainforest of Yucatan. There he joins the hunt for a lost Mayan city. But in the dense cover of the jungle a band of vicious convict mercenaries are waiting to strike...