In Like Flynn(2005)

Rhys Bowen

Fledgling private investigator Molly Murphy's latest assignment gives her the opportunity to escape the typhoid epidemic sweeping across New York City in the summer of 1902 for the lush Hudson River Valley. And it comes from an unlikely source-Captain Daniel Sullivan, a New York City police detective and erstwhile beau of Molly's. She has vowed to keep him at arm's length until he can rid himself of his socialite fiancee, but she can't pass up the chance to take advantage of his offer of a real detective job.
Daniel hires Molly to go undercover inside the country household of Senator Barney Flynn, in Peekskill, New York. Flynn's wife, Theresa, has become the latest devotee of a pair of spiritualists known as the Sorensen Sisters. The frail Theresa is desperate to use the sisters' alleged abilities to hold a seance to contact her infant son, who was kidnapped five years ago and never found; the accused kidnapper was killed before he could tell police where the boy was being held. But the police are sure the women are frauds.
When Molly allows herself to be distracted from the Sorensen Sisters and the members of the Flynn household by the unsolved kidnapping, it is a race against time to find out what's really going on before it's too late.
"In Like Flynn "is the latest captivating installment in a series which has garnered an impressive array of awards and nominations in just three books: Rhys Bowen's Molly Murphy mysteries have won the Agatha Award, the Anthony Award, the Bruce Alexander Historical Award, and the Herodotus Award, and have been shortlisted for the Agatha Award, the Macavity Award, and the Mary Higgins Clark Award.