In the 20th Century the teenager emerged as a separate species. But how? Was it the promise of sex? The power of pop? Or the pull of a 50cc Japanese two-stroke? James May is on a journey to find out. First up is fashion. The 20th century introduced fantastic new fabrics in fantastic new colours thanks to synthetic materials like Nylon. James tries his hand at making some for himself with some success. Close to James’s heart, of course was teenage transport, offering liberation from parents and the home. When he was a teenager he always dreamed of owning a very special motorbike, the Yamaha FS1E. The Fizzy. "The problem was of course, was that my mother would rather I played with something like a used hypodermic needle. The FS1E – a motorcycle you could ride at 16 - was just a symbol of death. It was like your son’s tombstone placed before you. It was ‘Not Allowed’." Finally he checks out the origins of the electric guitar – that potent symbol of teenage rock music. Who better to explain its power than the oldest teenagers in town Francis Rossi and Rick Parfitt of Status Quo. As Rick explains: "It’s just the magic of plugging into an amplifier. You put on a vibrato and you could sound good even if you weren’t. Volume is like speed – you buy a fast car because you want to be faster, you buy a big amp because you want to be louder…."

Each day, 180,000 people move into a city somewhere on the planet. In Big City, Bright Lights, James sets out to discover how we’ve created this high-rise, 24/7 experiment in urban living. He heads for New York – to the top floors of the Woolworth building, once the tallest building in the world. It’s being renovated, but how strong is it? To find out he decides to drop a 1982 Mini 1000 onto a plate of skyscraper glass. At the start of the 20th Century there was no national grid, no agreed system of voltage and James discovers that in 1922 there were 22 different plugs used across the country. Until a Geordie electricial engineer, Charles Merz, came up with a master plan: "The Merz mantra was unprecedented. One nation. One voltage. One plug." But there’s one light bulb James wants to find out about – one that was invented in the 20th century: "There’s one form of light that radiates come-hither hues to all those who are looking for some action… This light tempts you to the dark side! You won’t see a neon sign on a Methodist church or a lending library. Some unwritten convention says neon is used to advertise illicit pleasures that happen late into the night…" He meets master neon-bender Steve, as he attempts to make a neon sign for his favourite restaurant, his local kebab shop.

In Take Cover, James looks at how warfare drives ingenuity and gets to fly in the RAF’s latest supersonic jet. It’s an experience that he describes as "the most amazing thing I have ever done". The film begins by looking at the early days of air war at the start of the 20th Century. James flies in a biplane to get to grips with how difficult it was for the early aviators to hit any targets. Using flour bombs, he tries to hit a target on the ground. It’s a lot more difficult than he imagined. He also meets a group of ex-Paras to try some "make up for men", camouflage paint. When he fails to spot the Paras hidden in the woods he turns to modern technology for help. James moves on to look at "the biggest art show of the century", one of the most curious innovations to come from the military world. It’s called dazzle camouflage, and it involved painting warships in a confusing series of lines and stripes. Thousands of ships were painted like this to confuse German U boats during the First World War. Finally James meets up with Squadron Leader Paul Godfrey. He’s been invited to fly in the Typhoon, the RAF’s latest jet fighter. He has a private pilot’s licence - but only at 4,000ft at 120 knots. The Typhoon is a plane that can go from a standing start to six miles high in 150 seconds. After landing James admits he was slightly emotional: "Well, I admit I was a bit nervous when we set off but, absolutely unquestionably and not anything to do with bigging it up for television, that was the best thing I have ever experienced. It is, it is breathtaking, it really is, I can’t really describe what it’s like. It’s life-changing, frankly."

James sets out to discover how far he can push his body and finds out about some of the most remarkable medical advances over the last hundred years. He begins by testing himself in a centrifuge – a machine that can make fighter pilots and astronauts break out in a cold sweat. He wants to find out what would happen to his body when it is subjected to high forces. As he reached 4.4 g – he passed out: "There was no doubt that I’d clearly reached my limit. The blood was forced from my head to my feet and I passed out." He then tries out anti-g trousers, and manages to get to 5.4 g without passing out. Next stop is New York where James meets a group of athletes that have pushed their bodies to the limit to get extraordinary results. These elite sportsmen and women have each lost a leg – but are able to run long distances at high speed thanks to hi-tech prosthetic replacements. They are now winning against able-bodied competitors, a success which has brought the remarkable complaint that the disabled athletes may have a competitive advantage because of their artificial limbs. Back in the UK James is invited to watch open heart surgery - and sees a man’s heart come to a complete stop during the operation. But James’ biggest surprise came when he looked at one of the 20th century’s greatest medical breakthroughs – the discovery of DNA. He had his DNA tested: "To be honest I’m so English that I’m assuming I’m descended from a piece of fruit cake and cricket bat, but let’s see." The results, however, were not at all what he expected.