The reluctant reformer

The Lady X, a masked courtesan, is reputedly a noblewoman who's fallen on hard times. Lord James knows Lady X--but does not know she is Lady Margaret Wentworth, the feisty sister of his best friend who had forced James to vow to protect Maggie. But is she? When he tracks her down to a house of ill repute, what other explanation is there but that Maggie is London's most enigmatic wanton?