Fever dream - Douglas J. Preston

At the family home in Louisiana, FBI Special Agent Aloysius Pendergast is laying to rest his wife's possessions - a job he's been putting off since her tragic death twelve years ago. But whilst examining her property, he makes a startling discovery - one that leads him to believe Helen's death was not accidental...

With the help of his trusted friend Lieutenant Vincent D'Agosta, Pendergast embarks on a quest to uncover the mystery of his wife's final days. It's a journey that takes him deep into the dark heart of her past, to a hidden obsession and top-secret information that some people would do anything to protect. But as the hunt for Helen's murderer ventures into the Bayou, Pendergast find himself faced with a killer question: just who was the woman he married?