Murder on Amsterdam Avenue: Gaslight Mysteries, Book 17

In the midst of Sarah and Frank's wedding preparations, Sarah accompanies her mother on a condolence call to the Upper West Side, where the son of family friends has died unexpectedly. The father believes his son was poisoned and would like Sarah and Frank to look into the matter. They soon learn that not everyone wants to know more about Charles's death, and they also discover that they are in the company of a very present danger.