This is a sequel novel to the Scarlet Pimpernel. The second Pimpernel book written by Orczy, it comes (chronologically) third in the series and should be read after Sir Percy Leads the Band and before The Elusive Pimpernel.(Summary by Wikipedia)

Series:
1: The Scarlet Pimpernel
2: I Will Repay
2.5: The League of the Scarlet Pimpernel
3: https://librivox.org/search?q=elusive pimpernel&search_form=advanced
4: El Dorado: Further Adventures of the Scarlet Pimpernel
5: Lord Tony's Wife
6: The Triumph of the Scarlet Pimpernel
7: Sir Percy Hits Back
Prequel: The Laughing Cavalier