The Time Lords really ought to charge Doctor Who for not having a valid MOT certificate for his TARDIS. TARDIS malfunctions have become a regular feature of the programme, the first occurring in the third serial, "The Edge of Destruction". Most of these in later seasons involve the TARDIS materialising somewhere other than its intended destination, or in the wrong time period, but the malfunction involved in "Planet of Giants", the first serial of the second season, is of a rather different nature.
The Doctor, together with his granddaughter Susan and their companions Ian and Barbara, end up exactly where they want to be- in England- and at the right time period, 1964. The problem is that they materialise at the wrong scale, meaning that they are only one inch high. They have to struggle to survive in a world full of gigantic creatures such as ants and flies and, worse still, cats.
They also find themselves mixed up in a murder case. The house in whose garden they have landed belongs to an industrialist named Forester whose company are developing a new insecticide named DN6. On the day they land, Forester receives a visit from a scientist called Farrow, who informs him that he has written a report recommending that the British government do not grant a licence for the manufacture of DN6 on the grounds that it is far too deadly to all forms of invertebrate life, including such beneficial creatures as bees and earthworms. Forester, realising that this development will ruin him financially, shoots Farrow dead before he can send his report to the government. The Doctor and his companions therefore have three priorities- to survive as Lilliputian beings in a Brobdingnagian world, to return to the TARDIS and to normal size and to ensure that Forester's crime does not go unpunished.
This was an unusual theme for a "Doctor Who" serial, and I cannot think of another one quite like it like it, although there were to be later serials with an ecological theme, such as "The Green Death" and "Inferno", both Third Doctor adventures. The writer Louis Marks was clearly inspired by Rachel Carson's book "Silent Spring", which had come out two years previously and had started a political debate on the effects of pesticides on the environment and on environmental policy in general. Marks continued the trend, already apparent in the last two serials of Season One, of softening the character of the Doctor, who in the early days could often come across as a grumpy old curmudgeon, and showing him to be capable of courage, resourcefulness and altruism. The programme makers also seem to have spent more than their normal paltry budgets in the creation of the special props needed to create the illusion that the Doctor and his companions were only an inch high. Overall a very enjoyable serial. 8/10.