The Mystery of the Spirits - Snow & Winter, #5

Antique dealer Sebastian Snow and Homicide detective Calvin Winter have been happily married for a year and a half. In that time, there's been nary a mystery in sight, and for a recovering sleuth like Sebastian, an uneventful life is exactly what he needs. That is, until Calvin's lieutenant enters the Emporium and demands insight on a bizarre object known as a spiritoscope, hailing from the early days of the Spiritualism movement.
Sebastian's extensive knowledge of Victorian curiosities leads him to consulting for the NYPD-putting him at odds with his husband. And as the bodies begin to stack up, so do the seemingly dead-end clues, which if Sebastian can't make sense of, might result in a whole lot more death. Mystery, murder, and marriage. Sebastian's back.