Flashback by Nevada Barr

Park Ranger Anna Pigeon is filling in temporary duty at Dry Tortugas National Park in southern Florida. Enjoying the sun, Anna is settling in for some quiet time. Upon receiving a packet of letters from her sister written by a great-great aunt who lived at the fort with her career soldier husband, Anna spends her quiet evenings catching up on history. The tranquility is broken when a ranger fails to report in after his shift. Which follows a mysterious boat explosion. Feeling out of sorts and foggy, Anna tries to keep her wits about her, but secrets abound and mysteries are revealed. Not a bad read.