He has to do so in 'The Massacre', where Hartnell can't appear as both the Abbott and the Doctor; he has to do so in 'The Daleks Masterplan' when Hartnell is again absent; and also in 'The Time Meddler' - at a point at which he's only been in the Dr Who series for a mere 3 weeks!

If they could have squeezed the poor guy into 'Mission to the Unknown' (in which not only Hartnell but ALL of the regular cast was missing!) I'm sure they would have.

Happily, Peter Purves has real style and a ready wit, and never seems phased by what must have been rather a daunting prospect. Here, the Celestial Toymaker waves his hand and the Doctor becomes invisible for a couple of episodes (a pretty neat trick on an audio recording!), and is represented in the middle two episodes of this serial only by some occasional pre-recorded dialogue, leaving Steven and Dodo to give the Toymaker the runaround for a fortnight.

It's an enjoyable romp, enlivened too by the presence of Carmen Silvera (from the tv series 'Allo 'Allo) and that fine old character actor Campbell Singer, as our heroes' opponents in a series of deadly games, loosely based on children's nursery rhymes. And of course, to the youngsters in the audience in the 1960's, this gave the serial a particular edge - being menaced by their toys, which come to life and then try to kill Steven and Dodo.

On the surface, to us now as adults, the story is just a charming fantasy. But with playing cards, nursery rhyme characters and Billy Bunter all coming to life at the drop of a hat, and turning out to be lethal, it somehow didn't seem quite so harmless at the time...