Penance for the Dead by Cara Devlin

Principal Bow Street Officer Hugh Marsden is used to living in the shadow of disgrace. First, as the illegitimate son of the late Viscount Neatham, and second, as the man who permanently maimed his half-brother in a duel six years ago. Reviled by the posh ton, Hugh happily severed ties to polite society—until the enigmatic Duchess of Fournier, Audrey Sinclair entered his world and turned it upside down.

Now, Hugh’s half-sister Eloisa has done the same. Just days after returning to London and hiring him to find a missing person—someone Eloisa claims holds a destructive family secret—she is murdered on a ballroom floor. The prime suspect? Hugh Marsden.

When Audrey learns the Bow Street officer she’s come to cherish is on the run and being hunted for the crime, she vows to clear his name, no matter what it takes. Restricted to clandestine meetings, Audrey and Hugh’s investigation to find Eloisa’s true killer peels back years of Neatham family secrecy and a diabolical scheme to conceal the circumstances surrounding Hugh’s birth.

The killer will stop at nothing to prevent Audrey and Hugh from unearthing the rest of the wicked truth—even if it means sending them both to an early grave.