This, as I recall, was a nifty item. Attempting to fix the TARDIS (this is when he was stranded by Earth by the Time Lords), the Doctor ends up in a Mirror Mirror alternate universe. Here Britain has gone full-out fascist, only the Brigadier doesn’t have a beard, he sports and eye patch. They are also plagued by devolved men. One of the grimmer episodes for the time, and a mark of the show becoming a bit more hard-edged.