The one where we find out who Ringwood, Smallbeer and Gurney were...
I'd only ever really known George A Cooper as the interfering caretaker Mr Griffiths in BBC school drama Grange Hill before I found him in Doctor Who, so it's quite a surprise to find that he gives very good, convincing villain. He makes Cherub a thoroughly unpleasant character, and although he does sometimes stray a little too far over the top in his performance, he's certainly one of the best baddies of the Hartnell era. If he'd introduced a little more balance to his performance, toning it down at times to make him more quietly threatening, it would have been spot on.
If Cherub is a shouty, snarling bully, then Captain Pike is merely all these things in a frilly shirt. Michael Godfrey pleasingly does manage to bring light and shade to Pike, coming over as broodingly nasty one moment, and outrageously demented the other. It seems as soon as Pike uncovers Avery's hidden gold, he turns into a swivel-eyed monster, possessed by greed and obsessed with betrayal in the ranks. He seems hellbent on murdering the Doctor (aka Sawbones), and the energy Godfrey puts in to his final scenes is unsettling to hear!