The Red Lotus by Chris Bohjalian

A young couple are on a bike trip in Vietnam when the unthinkable happens - Austin, who is a proficient cyclist fails to return after a solo bike ride. His girlfriend Alexis gets whatever help in finding him from the police, consulate office, and fellow bikers until sadly a body is found. She returns to the states and her job as an ER doc with unanswered questions and thinking that she really didn't know her boyfriend. As she prods deeper we see that there is so much more going on than meets the eye. You think you are reading about a relationship based on secrets and then at the turn of a page, you are immersed in an international thriller about deadly pathogens. A must for fans of Michael Crichton and Robin Cook.