Who is Miles Fitzwarren from A Monstrous Regiment of Women and what is their importance?

Miles Fitzwarren is a member of the London military and Veronica Beaconsfield's former fiance. When Miles returns from the war, he becomes a heroin addict, so Veronica breaks off the engagement. When Mile's sister, Iris, who is a Temple member, is murdered he reappears. Upon Mary's request, Holmes steps in to help Miles overcome his heroin addiction and get well.