Thank you to Vicki Delany, Crooked Lane, and NetGalley for an ARC of The Sign of Four Spirits in exchange for my honest review. In this 9th installment of the Sherlock Holmes Bookshop Mystery, Gemma Doyle must use her deduction skills to solve the locked room murder mystery that occurs during a séance. The quirky characters of Jayne Wilson, Donald Morris, Ashleigh, and Bunny Leigh are back to add further delight in solving this unusual (maybe even paranormal) mystery. I continue to love this series and enjoy Gemma's skills and reasoning in solving mysteries, which is a great help to her boyfriend and police investigator, Ryan, who asks for assistance. I will continue to read this series and hope many others will enjoy it as well.