This is one of the best episodes from the Gothic Hinchcliffe/Holmes era. It features UNIT, the horrific Zygons and a rather embarrassing Loch Ness Monster (obviously not the idea of it, but how the Skarasen - to give it its real name, turned out) which is the only let down in an otherwise faultless episode that should be regarded as a vintage slice of Doctor Who. This was written by Robert Banks Stewart and directed by Douglas Camfield who both also went on to do the excellent 'The Seeds of Doom'. It is also worth mentioning that the music score by Geoffrey Burgon is magnificently eerie, especially when the nurse escapes through the wood. He was also the composer used for 'The Seeds of Doom' which again was just as brilliantly eerie. Finally, aren't the Zygons a brilliant design concept for an alien race of creatures!