The Hollow of Fear by Sherry Thomas (2018) Berkley

The third volume of Charlotte Holmes brings her closest friend, Lord Ingram, in danger of the hangman’s noose.  She takes on not just two personalities; herself and Sherlock Holmes, but adds a third, a brother named Sheringford.  It’s a cold and calculated plot that involves characters at all levels of intrigue.  And she makes use of her companion’s contacts to create an elaborate setting to help her oldest sister.  We also get to meet Mrs. Hudson.