Heart of Fire — Linda Howard

A fabulous lost Amazon city once inhabited by women warriors and containing a rare red diamond: it sounded like a myth, but archaeologist Jillian Sherwood believed it was real, and she was willing to put up with anything to find it - even Ben Lewis. Ruffian, knock-out, and number-one river guide in Brazil, Ben was all man - over six feet of rock-hard muscles that rippled under his khakis, with lazy blue eyes that taunted her from his tanned face...Jillian watched him come to a fast boil when she refused to reveal their exact destination upriver in the uncharted rain forests - and resolved to stand her ground. Neither of them could foresee what the days ahead promised: an odyssey into the fiery heart of passion and betrayal, and a danger that would force them to cast their fates together, immersed in the eternal, unsolved mysteries of love...