The Duke’s Decision by Fenella J. Miller

The Duke’s Decision is the second book in The Reluctant Duke series.
Lady Sarah finds Captain Paul Marchand, the Provost Marshal sent to arrest Mr O’Riley as a deserter, an attractive gentleman but is, of course, not about to throw her cap in his direction. She is more concerned with her mama’s extraordinary behaviour and with planning the wedding of her sister, Amanda, to Richard, the Duke of Denchester. Events do not turn out as planned and when Paul resigns from the military everything changes for both of them.