Anastasia and the Duke by Claudia Stone

When a midnight encounter with a duke almost lands her in Newgate, orphaned Hannah Smith realises that she must bring her career as a thief to an end – before she finds herself at the wrong end of a noose. But escaping the Seven Dials and Sidney Pritchard, the self-styled King of Thieves, is no easy task and Hannah finds herself persuaded into one last swindle; one which will set her up comfortably for life. If she can carry it off, that is…

Oliver Edward St Martin De Vere, Sixth Duke of Hawkfield, takes one look at Lady Lansdowne’s new companion and recognises her as the thief he shared a kiss with, one fateful night.
The thief he hasn’t been able to stop thinking about since.
Despite his desire for Hannah, Oliver vows to protect the elderly Lady Lansdowne from another schemer out to exploit her grief at the loss of her granddaughter, Anastasia.
The young woman is a fraud, and Oliver is determined to expose her – providing he doesn’t lose his heart to her first.