As the tale is an adaptation of the Conan Doyle tale "A Case Of Identity". Isabelle is the modern day version of Mary Sutherland; naive, well spoken, and completely under her step-fathers thumb. She comes to Holmes after her fiance disappears on their wedding night.
Holmes soon realises a number of irregularities that lead him to believe there never was a fiance, only her step-father in disguise. He eventually confronts the stepfather on his deception, and although he knows there is nothing that can be done by law to Mr. Devon, the impending threat of using his cane in a painful manner persuades Devon to scuttle away, never to be seen again.
Maddie Moate was going to appear in the 1893 set episode, "The Creature In The Rye" as Lady Violet Kensington, an ancestor of Isabelle. Although it is not seen in close up, the photo Mycroft Holmes has for Violet is that of Maddie Moate. However, due to a commitment filming as an O2 Guru, Maddie was unable to fit the role in. The role was subsequently recast to Victoria-Jane Appleton (who would play Miss Bliss in Reign Will Fall), who pulled out one day prior due to illness. This resulted in a last minute recasting with Cassie Parkes eventually taking the role - with just 10 hours remaining till shoot.