"Shada" was written by Douglas Adams -- yes, that Douglas Adams -- and was meant to be the final episode of the seventeenth season. But a strike brought production to a halt, and by the time the labor action was settled, it was too late to resume production, and when a new executive producer was brought in at the beginning of the 18th season, he decided to shelve the project. The completed footage was eventually released on home video in 1992, along with a script book so viewers could fill in the missing scenes. And Adams cannibalized parts of the script for his novel Dirk Gently's Holistic Detective Agency.
"Shada" was originally written for the fourth doctor, Tom Baker, but for this new production the BBC decided to use the eighth Doctor, Paul McGann, who I thought was quite good in the Doctor Who movie that aired on Fox a few years ago. They worked with the Douglas Adams estate to update the script for the new Doctor.
I'm very excited by this. I've been a Doctor Who fan for -- good Lord! -- 22 years, and while I'm pleased that the BBC has kept the franchise alive through books and radio programs, I've always wanted to see it return to television, with the kind of production values it deserves. This information is good news; if "Shada" is a success, maybe they'll do more webcasts and eventually return it to TV, where it belongs.