The one where a gibbering tramp makes first contact with an alien species...
The episode opens very similarly to Spearhead from Space, with an unidentified mass approaching Earth and being picked up by UNIT technicians on radar. Although he's a pretty poor actor, Michael Walker (as Harry, according to the novelisation) is very easy on the eye and manages to make it past this first scene to feature in two entire episodes. Was there an effort to introduce a wider "UNIT family" in Season 8 to back up the Brigadier, Captain and Sergeant, what with the introduction of Corporal Bell in The Mind of Evil, who also features here? I like Harry: he can stay...
It's a damn good opening to the story actually, showing a weird alien mass (ship?) approaching Earth like some giant galactic puffer fish (it even seems to have breathing "gills"). The glimpse we get inside the ship is a nightmarish collage of cross-fades and superimpositions of various strange organic beings. It's truly alien and I love it.








