Inspirations - Planet of Giants

The first story of Doctor Who's second season, though it was made before the short summer break. It owes its origins to the programme's prehistory, for a story in which the Doctor and his friends were shrunk to diminutive proportions was almost the show's opening adventure.
The three types of story which the programme could show were to have been backwards into the past, forwards into the future (or to alien worlds - held to be always in the future), or "sideways". The latter meant subverting the ordinary, and could be set in the present day. An idea for the very first story - commonly referred to as "The Miniscules" - had the TARDIS take the Doctor, the two teachers and their pupil to Ian's (Or Cliff's, as he was then) science lab at Coal Hill School. The travellers would find they were only one inch tall, and would have to navigate the classroom to get back to the safety of the ship. They could drown in a sink, be burned by Bunsen-burners, or be trapped in a matchbox by one of the pupils.
As the debut broadcast date approached, it was realised that the effects needed to pull this off successfully required more planning to develop. The idea was shelved, to be revisited later. The original storyline was devised by C E "Bunny" Webber, one of the series' forgotten heroes. It was then given to writer Robert Gould to develop, but that also fell through. Sydney Newman had reservations about the giant insects that would plague the travellers - fearing they would be too close to 1950's giant insect B-movie monsters - his detested BEMs. In the end the idea went to Louis Marks, and he came up with the four episodes that comprised Planet of Giants. Marks had written for soaps and one-off drama series, but his real interests lay in Renaissance history. He had written an academic piece about the economy of late medieval Florence. He'll later be asked to stick Daleks in a temporal paradox story, rewrite Forbidden Planet / The Tempest / Jekyll and Hyde, before finally getting some of his real interests on screen.

In September 1962 Rachel Carson produced a book called "The Silent Spring". This science tome dealt with the detrimental effects of pesticides, which she felt were being widely used without proper study of their long-term effects. She argued that the big chemical companies were unduly influencing governments - putting people at risk for the sake of profit. In particular, Carson was concerned that pesticides were killing those insects essential for plant propagation, as well as the pests. This would have a knock-on effect up the food chain, affecting birds and other animals. If left unchecked, one day there would be a silent spring, when no insect chirruped or bird sang. Naturally, the chemical giants complained, but the US public had their eyes opened, and the common pesticide DDT was banned. The book helped towards the creation of the US Environmental Agency - that body which the current POTUS seems determined to undermine. Marks obviously read the book, and had the same concerns, and hence the creation of the scientist Smithers and his business partner Forester.
Unusually, Marks structures his story in such a way that the TARDIS crew and the full sized human characters never once interact, though the actions of each influences the other. Smithers and Forester only inadvertently threaten the miniaturised time travellers, and the Doctor's party decide to fight against them without knowing anything about them, personally. They are primarily battling the new chemical - DN6 - in order to make sure it doesn't kill all the useful insect life. They know that they are in the grounds of a house that is occupied by a murderer, but have no idea that the creator of DN6 is present, save for finding its chemical formula scribbled on a notepad. They make quite a leap in assuming that the two things are connected.

Jeopardy is added as Barbara rather foolishly picks up a seed that has been coated with DN6 - even though there is enough evidence to show that it is toxic. This provides an element of "race against time". They can't spend forever trying to work out how to warn against DN6. The obvious thing would have been to let Smithers know that his chemical is killing the useful insects, but that avenue is blocked by Forester's murder of the civil servant Farrow, who had planned to prevent its production.
There is some argument as to when the Doctor starts to become the character that we know today - the crusader who will fight injustice wherever, or whenever, he encounters it. Some have seen it in his decision to venture into the aqueducts of the planet Sense-Sphere. He could simply have let the Sensorites sort this out for themselves. All other stories so far have seen the Doctor act purely to regain his TARDIS, or free his companions - primarily his grand-daughter.
Here in this story, the TARDIS crew have the chance to get back to the ship, and need to do it quickly as Barbara could die otherwise, and yet the Doctor decides that a stand must be made. This is helped by Barbara herself urging her friends to do so, despite the risks to herself.

The Smithers / Forester / Farrow half of the plot is lifted straight from a police show, like Z-Cars or Dixon of Dock Green. Had the story not been cut down from four to three episodes, there would have been a lot more of Smithers and Forester becoming increasingly suspicious of each other (mainly due to the acts of sabotage by the TARDIS crew), and the roles of local switchboard operator Hilda Rowse and her policeman husband Bert would have been enhanced. More would have been made of how Hilda worked out that Forester was impersonating Farrow. As it was broadcast, Hilda seems to make some incredible intuitive leaps.
Setting a fantastical element against a common crime caper puts one in mind of shows like The Avengers, which will later have a miniaturisation plot-line, guest starring Nicholas Courtney and Kevin Stoney.
Other influences to look for must obviously include the 1957 film The Incredible Shrinking Man, which was based on a Richard Matheson story. The main character in this, his shrinking caused by exposure to a radioactive cloud, also has trouble with a domestic cat, though it's the fight with the spider that most folks remember. Planet of Giants has some oversize insects, but they never actually threaten the TARDIS crew. Gould's scripts would have featured a spider.
It is significant that the story spends only one episode in the wilds of the garden, and the next two (should have been three) hanging around a sink.
The two cliffhangers are actually amongst the strangest in the show's history - threatened with being eaten by a cat, or being washed down a plug-hole. Who would have thought that the image of a man washing his hands with a bit of carbolic would lead into that famous music, and it would work.
Before parts three and four were edited together, it would have been shown that the cat would have also been killed by DN6. This caused alarm amongst the production team. Thals can be exterminated willy-nilly, but god forbid the children of Britain should be confronted with a dead Tiddles.

It is interesting to note that when Susan and the Doctor start to talk about being caught up in an air raid, there is a long enough pause for the viewers at the time to automatically think they are referring to the WWII Blitz. Bombs had been falling less than two decades before. The Doctor then mentions how terrible those Zeppelins were - pushing their adventure back to the war a generation before.
In the first episode, Ian speculates that they may have arrived in some sort of World's Fair. These huge events did often feature special displays wherein visitors might have been expected to walk through an area where they saw oversize props, making them feel tiny.
A special mention for designer Ray Cusick for being able to realise this story on screen. Some of the insects had been created for another show, and there is a lot of use of characters being shown against photographs, but he achieves a lot of good effects in this. The photo technique involved the actors standing in front of a black drape in one part of the studio, and this camera image being superimposed over the photographic image. This tended to make the characters somewhat transparent, and it is the reason why the Doctor wears a white hat on Vortis instead of his black one.
Cusick claimed that the Bunsen-burner finale was partly due to him - being asked what was feasible to realise in studio. Others claim that it was always in the scripts.
Another special mention - Douglas Camfield has arrived. He directed the final of the four original episodes, and was allowed to get sole credit for the edited one broadcast.
Next time, THEY are back, the Unearthly Child leaves, and Terry Nation gets to exorcise more of his childhood wartime experiences...