In the Courts of the Crimson Kings by S. M. Stirlling

In an alternate world where life was discovered on both Venus and Mars in the 1960's, Mars has developed into a place where human ambassadors and scientists wrestle over the secrets buried in the Martian dust, where civilization was highly developed before humans were even raising Stonehenge.

Into this brave new world comes a young archaeologist, Jeremy Wainman, come to study some ancient ruins of a place the Martians call "The Deep Beyond", where the red-green plants that help sustain the Martian atmosphere grow thin and weak from lack of water. But Jeremy won't be alone on his expedition. With him comes Sally Yamashita, a colleague who may also be in pay of the US Intelligence, and Teyud za-Zhalt, a mercenary of the Thoughtful Grace caste who is hiding a secret of her own. She is a product of the unlawful union between a member of the Thoughtful Grace caste and a member of the ruling family.

While her lineage is generally not known, there are those who pursue her for her eggs as well as her head. Every step along the journey they are pursued by those who wish to wrest her life and genetic secrets away from her. But when the expedition finds the secret of secrets buried in a long-forgotten Martian city, the alien artifact known as the Invisible Crown of the Crimson Dynasty, there will be another reason to find and kill Teyud, to gain the crown that can only be removed with her death.

Separated, Teyud and Jeremy find themselves separately fighting for their lives, each trying to make it to the royal city, Dvor Il-Adazar for a final showdown which will determine who rules Mars: Teyud, or her enemies.

This book was not a long one, but it was filled with story and background on Mars. Mars was intriguingly different, with much of their "technology" being biotech: animals or plants grown for a certain purpose. Even such things as vehicle engines and syringes are purpose-grown, and can go feral, as sometimes happens in the deep beyond. Fights are filled with menace and danger, and even though Jeremy has an advantage in strength and muscle power (growing up as he did on Earth, which has a higher gravity than Mars), this doesn't guarantee him success in his fights.

The romance of Teyud and Jeremy is handled well, and feels organic to the story, i.e. not imposed on it by the author, and its conclusion is satisfying. In fact, the entire story is very well done, and is something readers of science fiction, or speculative fiction, would enjoy. A very well-done book.