Great television shows are always trying to do something different and innovative, they want to play with their characters and put them in different situations to see how they cope. One of the most interesting things you can do with a show is to completely change what people know by creating an alternate universe, especially if the show is sci-fi or fantasy. It simultaneously wrong foots both the characters and the audience, and allows the writers to ask one of their favorite questions: "What if?" That said, there are a lot of shows who abuse this concept, so much so that the idea of the alternate universe has become a trope in and of itself. While I'm a sucker for alternate universes, the fact that so many shows turn to them has taken some of the novelty away. It has become harder and harder for writers to create a really solid episode around the concept. So when you find one that is imaginative and detailed, one that uses the established characters so brilliantly, it really stands out. Alternate universes can fall flat on their faces, but when done correctly, a lot of people will cite them as being their favorite episode of a given show. No guts, no glory, right?
10. Doctor Who - "Inferno"
In the Doctor Who episode Inferno, the Doctor is trying to convince a mining operation that they should halt their work. Surprise, surprise: it's 1970s Doctor Who and there's some kind of mining crisis going on. Apparently digging into the Earth's crust will spread an infection that turns people into weird, hairy, green monsters. The Doctor is sent into an alternate universe, where the mining work is slightly ahead of his original world, which means he has the opportunity to see what will happen if they continue unchecked. Bad, bad things happen. But what's truly interesting about the alternative universe in Inferno is not what's explicitly shown, but the subtext. They're obviously living in some kind of totalitarian regime, which means that somewhere along the line, something major happened that Britain away from a constitutional monarchy. Maybe Hitler won the war. Maybe some prime minister along the way got a little too much power and set up their own fascist government (not naming any names, but in this scenario I think we all have to admit it was probably Thatcher). But the point is, we're not really sure where the deviation occurs, which makes this whole story especially intriguing. Meanwhile, we've got angry Brig with an eyepatch and a super severe Liz Shaw who is absolutely a dominatrix in her off hours.