Leah Andrews is an archaeologist. Jack Hobson is a climbing guide.
To get one thing settled immediately, the two individuals who would find themselves up against all sorts of troubles from several countries and intelligence agencies were not together when the circumstances which lead to the first trouble started but they already knew each well, perhaps too well. They had once been married. Technically, though they were no longer together, they were still married but it was not something either mentioned very often.
The Dr. Andrews we first meet is an adventurous sort, standing as she in a thunderstorm atop a crevasse in the Gila National Wilderness, technically a trespasser who needs to keep one eye out for the Park Rangers, one at the weather, and one at the huge drop she is about to repel down into. She will make that climb down and then make a discovery that could make her world famous in her field, or a resident of a federal prison for being where she was not supposed to be, or dead from those who really did not like what she found.
The Hobson in question is a world-renown climbing expert, a man who had summit-ted just about every peak there was in every continent there was, including Antarctica. When we first encounter him, he is helping a billionaire achieve his dream of reaching the top of Mount Everest.
The find that Andrews would make would require an expert in climbing which would force her to reluctantly ask for his help and would put both of them in a whole lot of danger.