This prequel had been rumoured, but I’m delighted to see it’s true:
But it really makes me want to see more of McGann’s Doctor. One tv-movie plus one minisode is not enough.
If you’re wondering who the Sisterhood of Karn are, go watch “The Brain of Morbius” (wherein the Doctor describes Karn as being about two billion miles from Gallifrey, which would most likely place it in the same solar system – that being about the distance between Earth and Uranus).