There was no Duke or Duchess of Monmouth during Victoria's reign. There had been one in the mid 17th century, the eldest illegitimate son of King Charles II, who led an unsuccessful against his uncle, King James II. The ones portrayed here are fictional.
A Damascene Conversion, refers to Saul on the Road to Damascus, who eventually became Paul after receiving a vision of Jesus, and as a result he transformed into an ardent supporter of Christianity. Before his conversion, as a Jew he persecuted other Jews who accepted Jesus as their Lord and Savior.
Throughout this episode, a jaunty orchestral waltz piece is played which is reminiscent of Dmitri Shostakovich's "Jazz Suite", though this was not written until 1934, almost 100 years later.