Ishmael's Star was an unproduced P.R.O.B.E. film written by Mark Gatiss. It would have been the third and final P.R.O.B.E. film, serving as a prequel to The Zero Imperative and The Devil of Winterborne, about how Liz Shaw retired from Cambridge. It was going to be about "a war criminal who had some plan about a comet". Gatiss had Jeffrey Holland in line for the titular character.
Gatiss wrote half of the script before it was cancelled by Bill Baggs, who deemed it too expensive. (REF: Downtime – The Lost Years of Doctor Who)
A war criminal named Ishmael later appeared in a 2021 BBV Productions Dionus's War audio story, Call Me Ishmael.