Lady Isabelle is a noblewoman who is the guardian of her sister-in-law Iris (Lucy Speed). She tells Iris that her intended husband, Thomas of Glockshire (David M. Morizot), has died in the Crusades. She then arranges for her to marry the evil Lord Garth (John Forgeham).
Lady Marion Fitzwalter (Anna Galvin) breaks into the castle and rescues her cousin Iris who is under the hypnotic trance by Isabelle. However, Isabelle who still has power over Iris, tells her to return. In the meantime, Isabelle has captured Thomas and Robin Hood and his men. Marion returns to the castle to break them out.
In the end, Iris takes the pendant that Isabelle has been using for her hypnosis powers. Then Marion throws a pie at Lady Isabelle. The last scene we see of Isabelle is of her and Lord Garth shackled in the castle prison.
- Kate O'Mara earlier appeared as the henchwoman Lisa in the 1969 episode "Stay Tuned" in the TV series "The Avengers".
- Kate O'Mara appeared as the handmaid Alys in the 1970 Hammer Horror film, "Horror of Frankenstein".
- Kate O'Mara appeared later on stage in 1971 as Madame Gerda in the adaptation of the classic British TV series "The Avengers: Stage Play".
- Kate O'Mara appeared as The Rani in the British science fiction TV series "Doctor Who". Her character appeared in 1985 and again in 1993.
- Kate O’Mara appeared as one of four actresses who played Mrs Elizabeth Peacock in the classic ‘90s game show ‘Cluedo’. She played the part in season two.