|Planet of Origin:||Kayaclasch|
|First Appearance:||A Timeless Man|
|Last Appearance:||The Crime Sports|
|Portrayed By:||Honor Blackman|
Susannah's relations with her fellow Infinity Knight were never fully explained, although she acted at times like both his superior and auditor. After a few adventures together, she was recalled to Kayaclasch. She reappeared in "The Crime Sports" as a (clearly unwilling) witness against the Inspector.
Much later in the programme's run, it was strongly hinted that the Instructor was her new incarnation and/or replacement.
- The real-life reason for the character's abrupt and early departure was that she simply wasn't working as well as originally hoped, and the decision was made to give the Inspector human Associates who would serve as audience surrogates. The Inspector Spacetime producers always strongly insisted that Ms. Blackman was not the problem with the character, while the actress herself went on record in Inspector Spacetime Magazine that her leaving was as amicable as possible under the circumstances, and that, unlike her character, she was quite happy to return for the aforementioned cameo when her schedule allowed for it. She did however turn down the opportunity to revive the character in audio plays, and the voice role was thus re-cast with Maureen O'Brien.
- Upon leaving the show, Ms. Blackman was immediately hired to play Cathy Gale on the television programme The Avengers, giving her the perhaps unique distinction of being a lead player in two seminal British series in the same year.