The Price of Lemon Cake by Jennifer Ashley

When Kat Holloway approaches Lady Bobby Perry and Judith Townsend to help her discover what a young aristo is getting up to in a gentleman’s club, Bobby quickly accepts, coaxing a promise of Mrs. Holloway’s stupendous lemon cake in return.
But the investigation quickly turns into more than a simple spy mission, forcing Judith to confront a painful part her past. Both Judith and Bobby must bring their own unique skills to help Kat solve the tricky and dangerous problem.