This ranks with Castrovalva and Earthshock as one of the three masterpieces of season 19, only in this case, the script and the acting are the be all and end all, as the production values are a little plain, and in some cases, barely adequate at all. Having said that, the acting is SO GOOD and the dialog in particular is so STUNNING that it leaves most other Dr.Who looking pale by comparison. Simon Rouse gives one of the essential guest performances in the show's 26 year history as the mentally ill and genuinely unnerving Hindle (great name!) while Mary Morris is perfect as the wise woman. Janet Fielding is outstanding as Tegan, explored in a way no other companion ever has been, and the guy in her head, who represents the Mara is creepy like your worst nightmare. With juicey lines like "By the way, one thing: you will agree to being me...sooner or later...this side of madness or the other!" Director Peter Grimwade delivers this theatrical piece with a pace that was ahead of its time and he excells in the scenes in tegan's mind, a total blackness filled with whited out, over exposed freaks and grotesques with snake emblams on thier flesh. He symbolic rape as she fights for control of her mind and loses is proof of the brilliance of 80s Dr.Who as a whole and the Davison era in particular. Unmissable, must see stuff.