This week I'd like to expand on David's excellent topic from last week. How exactly do you pick out sci-fi episodes in a series like
The Twilight Zone - series that is predominantly thought of as sci-fi, but so often delves into other genres?
I've picked out "The Monsters are Due on Maple Street," "The Eye of the Beholder" and "The Gift" to try to explore this...
The Monsters are Due on Maple Street Season 1 - available now at Amazon (DVD/Blu-ray), HMV (DVD/Blu-ray) and Play (DVD/Blu-ray) 
A "meteor" flies over Maple Street and suddenly the electricity goes off and the cars all stop. The next thing you know, the residents of Maple Street believe that aliens posing as humans have come down to start an invasion and they begin turning on each other as they try to unearth who is human and who isn't - all because of one little boy's willingness to believe in science fiction stories.
An indictment of McCarthyism if ever I saw one, the residents of Maple Street turn on each other horrifically in their panic and paranoia, commiting assault and murder as they seek out those who are "different". Grown men accuse small children in their attempts to not be suspected themselves and the street eventually descends into chaos. The twist is, of course, that aliens (read: communists) are exploiting this paranoia to force humans to destroy themselves. Like a lot of great sci-fi of the period, "The Monsters are Due on Maple Street" acts as a brilliant allegory for the political tensions of the time, while bravely critiquing America's anti-Communist regime.
The Eye of the Beholder Season 2 - available now at Amazon (DVD/Blu-ray), HMV (DVD/Blu-ray) and Play (DVD/Blu-ray) 
A woman lies in a hospital bed, her face bandaged while she is treated by doctors and nurses whose faces remain in shadow. The woman is a "freak" who is waiting to see the results of an operation that will make her "normal" or else she will be exiled to a village with other "freaks". As it turns out, the woman is, by our standards, beautiful but the rest of the world is occupied by hideous, pig-like people.
Conformity is often the topic of great sci-fi. Think John Wyndham's novel
The Crysalids, any of the versions of
Invasion of the Body Snatchers from the 1956 classic to the 1998 re-interpretation
The Faculty, or even
Doctor Who's infamous antagonists: the Daleks and the Cybermen. "The Eye of the Beholder" deals with a dystopian society where everyone is encouraged - even forced - to look the same or else face exile.
Perhaps the scariest thing about this dystopia is that it's not a million miles away from the real world. It's just that here, everyone wants to look like pig-people, rather than the skinny beauties of glossy magazine culture...
The Gift Season 3 - available now on Amazon (DVD/Blu-ray), HMV (DVD/Blu-ray and Play (DVD/Blu-ray) 
"The Gift" takes a somewhat classic sci-fi premise of an alien coming to Earth, only to have his intentions grievously misunderstood by the humans he encounters - much like
The Day the Earth Stood Still. The alien arrives in Mexico and accidentally kills a police officer. As a result, he is persecuted and killed while the "gift" he bestows upon a small boy - the chemical make-up of a vaccine for cancer - is burned before it is read.
The episode plays on humanities' mistrust of anything different, our assumption that all aliens must be coming to harm us. It highlights that these assumptions say much more about us and our nature, than the nature of any "invading" force. Great sci-fi as ever, shines the light not on the behaviour of the aliens, but on our own behaviour and makes us ashamed to be human. That the only person to trust and befriend the alien is a small child has almost biblical connotations - another running theme in great sci-fi (I again point to
The Day the Earth Stood Still).
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That the episodes I have picked out are all sci-fi in one way or another is debatable - but that is largely because they straddle a variety of genres which makes it difficult for them to be pinpointed. So what makes sci-fi? Is it the presence of aliens or alternate realities?
Or is it a plot that by its very nature makes us examine ourselves through the context of others?
I'd love to hear what others have to say about this so please do contribute to the thread!
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Season 4 is also available now from Amazon (DVD/Blu-ray), HMV (DVD/Blu-ray) and Play (DVD/Blu-ray). Season 5 will be released 6 February 2012 and is available for pre-order from Amazon (DVD/Blu-ray), HMV (DVD/Blu-ray) and Play (DVD/Blu-ray).