An enjoyable episode, a bit like a serious version of The Ghost of St Michael's rammed together with the non-Zygon parts of Terror of the Zygons. Scottish aristocrats are always up to no good in film and TV drama. I'm not sure what the actual purpose of maintaining a massive submarine docking station is, or how likely it would be that the castle would have a system of suitably-sized caves beneath it, but still.
Steed's guise as 'Jock McSteed' lowers the tone rather. He's looking a bit tubby in that kilt.
Gordon Jackson is an absolute delight as Iain DeAth, hostility and propriety in perfect balance in his conversations with Mrs Peel.
Also seen: James 'Selris' Copeland. John Lucarotti at the typewriter.
