Mrs. Jeffries and the Three Wise Women by Emily Brightwell

Mrs. Jeffries and Inspector Witherspoon solve a holiday homicide in this mystery in the New York Times bestselling Victorian series.
Christopher Gilhaney isn't a popular man, and he proves why once again when he insults every guest at Abigail Chase's Guy Fawkes Night dinner party. When Gilhaney is shot dead under the cover of the night's fireworks, his murder is deemed a robbery gone wrong. But when the case hasn't been solved six weeks later, Inspector Witherspoon is called upon to find the killer-and quickly!
With Christmas almost here, Inspector Witherspoon and everyone in his household is upset at the possibility of having to cancel their holiday plans-all to solve a case that seems impossible. Only Luty Belle, Ruth, and Mrs. Goodge refuse to give up and let the crime become a cold case. In fact, the American heiress, the charming next-door neighbor, and the formidable cook use all of their persuasive powers to get the others on board, because these three wise women know justice doesn't take time off for Christmas.