Gravemould and Ectoplasm — Barbara Hambly

A novelette of 16,000 words, the follow-on to the Asher and Ysidro vampire series. Recently arrived in New York in the closing years of World War One, Lydia Asher and her friend, the "recovering" vampire Don Simon Ysidro, attempt to solve a puzzle that begins with a fraudulent seance, and rapidly veers into revolution and murder.