The Man on the Istanbul Train — Maria Hudgins

Dr. Lacy Glass is traveling by rail to an archaeological dig in central Turkey when she sees a man she befriended hours earlier fly past the window of the train. Dead. If not for her, he wouldn't have even been on the train so she feels responsible.
When she arrives at the dig she learns that the dig's backer, a wealthy American, has died there that same morning. Problem? Both men seem to have been named Maxwell Sebring.