A Ruse of Shadows by Sherry Thomas

Charlotte Holmes is accustomed to solving crimes, not being accused of them, but she finds herself in a dreadfully precarious position as the bestselling Lady Sherlock series continues.
Charlotte’s success on the RMS Provence has afforded her a certain measure of time and assurance. Taking advantage of that, she has been busy, plotting to prise the man her sister loves from Moriarty’s iron grip.
Disruption, however, comes from an unexpected quarter. Lord Bancroft Ashburton, disgraced and imprisoned as a result of Charlotte’s prior investigations, nevertheless manages to press Charlotte into service: Underwood, his most loyal henchman, is missing and Lord Bancroft wants Charlotte to find Underwood, dead or alive.
But then Lord Bancroft himself turns up dead and Charlotte, more than anyone else, meets the trifecta criteria of motive, means, and opportunity. Never mind rescuing anyone else, with the law breathing down her neck, can Charlotte save herself from prosecution for murder?