Fortune Favors the Dead, by Stephen Woodson

A female detective duo with Will Parker, a sometimes gender non-conforming spunky bisexual assistant, and Lillian Pentecost, a sophisticated middle aged butch with MS and a reputation as the best PI alive.
In the 1940s, the widow of a steel magnate is found dead at a Halloween seance, killed by a crystal ball. All accounts say she was alone in a locked room when this happened.
Could this be the work of her husband's ghost? The medium who lead the seance? Or the victim's daughter, who Will is quickly falling for?