The Edge Of Destruction-

[lonemagpie]

Bit of a mix, some silliness ("we saw that in the fourth universe"), the first big line-stutters from Hartnell, yet also very mysterious and with the final burst of character creation, getting everybody properly into their moulds (except Susan, who isn't allowed to be this develeped again). In particular, the Doctor completes his transition from abductor and potential caveman-murderer to the "never cruel or cowardly" (Well, until the late 80s) bloke we all know...

With the reveal of the problem, it would actually (if compressed) make a really good Twilight Zone style anthology one-off.