He was the librettist for one of the last Savoy Operas, A Welsh Sunset (1908), and had his greatest success with the musical comedy The Girl in the Taxi (1912).
During the next four years Fenn had three more full-length plays staged: A Married Woman (1902), The Age of Innocence (1904) and The Convict on the Hearth (1906).
[2] In the West End, Hilda Trevelyan had a great success in the leading role, and Fenn adapted it for the cinema in 1920 under the title Suds, a film that starred Mary Pickford.
[1][2] Of Fenn's later plays, the one that made most impression was The Girl in the Taxi (1912), a collaboration with Arthur Wimperis (libretto) and Jean Gilbert (music), an adaptation of a German piece, Die keusche Susanne (1910), which was based on Antony Mars and Maurice Desvallières's play, Le Fils à papa (1906).
[3] In 1906 Fenn collaborated as librettist with the composer Philip Michael Faraday on the comic opera Amisis, produced at the New Theatre.