Murder at the Seven Dials by Cara Devlin

A murdered opera singer. A duke drenched in her blood. For Bow Street Officer Hugh Marsden, the brutal killing is a straightforward case. Ever since his exile from polite society, the chance to arrest a high and mighty peer of the realm has never presented itself. Hugh won’t snub the opportunity now.
But Audrey Sinclair, the Duchess of Fournier, is certain her husband is wrongly accused, and she’s determined to prove it to the arrogant Bow Street officer, even if she must employ her most peculiar ability—or perhaps curse—to guide her investigation. After all, a duchess can do as she pleases.
Exasperated with the meddling duchess, Hugh is convinced she is protecting her own secrets, and the duke’s. But when Audrey’s discoveries persuade him to believe the true killer is still at large, he has no choice but to join her in the hunt—if only to keep her from becoming the next victim.