The Mystery of the Spirits by C.S. Poe

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, nothing more compelling than the curiosities that pass through his shop is exactly the kind of life he needs.

That is, until Calvin’s lieutenant enters the Emporium and demands insight on a bizarre Victorian object known as a spiritoscope, hailing from the early days of the Spiritualism movement. Sebastian’s extensive knowledge of all things strange leads him to consulting for the NYPD—putting him at odds with his husband, into a battle of wits with detectives, and pulled into a dangerous scavenger hunt across the city that, if Sebastian doesn’t step up to the challenge, will result in a whole lot of death.

Mystery, murder, and marriage… Sebastian’s back.