Planet of Giants opens with the Doctor fretting over the fact that the TARDIS doors opened just before the ship materalised.  He’s clearly extremely worried about this and it’s possible that the scripted anxiety seeped into Hartnell’s performance as he’s rather incoherent during the scene.  But once the Doctor calms down, Hartnell also seems to recover somewhat.

When they venture outside, the four split up (bad move, you’d think they’d have learned by now!) to explore and begin to puzzle over the strange things they see (such as giant earthworms and ants).  The audience, thanks to the episode title, is slightly ahead of the TARDIS crew but it takes the reveal of items like a huge matchbox to provide the final clues.  The Doctor has finally managed to steer the TARDIS back to Earth in the 1960’s but they’ve all been reduced to the size of an inch.

Ian’s slow to accept this, preferring to believe that what they’ve found are nothing more than advertising props, built for an exhibition.  Given all that he’s seen over the course of the first season it’s a little jarring that the rational Ian fails to grasp the truth.  However this does, for once, enable Susan to be shown to be the sensible one (although she still has her fair share of hysterical outbursts).

A minuscules story had been planned right from the beginning (originally it would have followed on directly from the first episode).  It’s a clear technical/design triumph – Raymond Cusick, on the show’s usual tight budget, works wonders (the glass-shot of the house is a stand-out shot).  The various dead insects are also impressive.

But the story tends to fall down with the sub-plot of the giants.  The trials and tribulations concerning the TARDIS crew’s attempts to return to the ship are fine, but they wouldn’t have been substantial enough to carry a four-parter by themselves.  So in this first episode we meet the single-minded businessman Forester (Alan Tilvern).  Forester has invested a great deal of money in a new insecticide called DN6 and he’s perturbed to learn that the man from the ministry, Arnold Farrow (Frank Crawshaw), is recommending that it doesn’t go into production.  The reason is quite simple – DN6 is an indiscriminate killer and wherever it’s applied nothing (not even insects) will survive.

Because the Doctor and his friends never directly interact with Forester and later on the deluded creator of DN6 (Smithers), there’s a disconnection between the two main plot-threads which is one reason why the story never quite satisfies.  But on a positive point, Tilvern is a suave villain who thinks nothing of shooting the unfortunate Farrow dead (which could be said to be a mercy killing, thanks to Crawshaw’s distracting speech impediment).