Karl Pilkington travels the world in search of answers to some of life's most important questions. He begins with marriage, wondering whether he is wrong about not wanting to tie the knot with his long-term girlfriend. In Delhi, he gains an insight into arranged marriages by going on a date with a prospective wife - and her parents - and in Bangalore, he is asked to help a pair of elite wedding planners. He also sniffs out a scientific approach to finding the perfect partner in LA, before searching for an alternative way of getting hitched in Las Vegas.

Karl Pilkington tries to find out how people achieve happiness, something he isn't sure it is worth pursuing. In Mexico, he joins members of a tribe who enjoy running ultra-marathons and meets a group that finds pleasure in pain. In LA he hangs out with some hip-hop clowns, experiences a day of beauty with a plastic-surgery addict and gives up his possessions to see if the simple life is the answer to contentment.

Why do people have children? That's the puzzler bothering world-weary philosopher Karl this week. Travelling the globe, he tries to understand why couples feel the need to become parents, visiting a fertility festival in Japan and a natural birthing centre in Bali - where he lends a hand with a delivery - and meets an LA couple looking to take the next step.

Karl aims to get to the bottom of his relative lack of a vocation, and visits an 85-year-old Japanese inventor to discover whether he has what it takes to become a genius. When the results prove less than encouraging, he sets his targets a little lower by trying his hand at becoming a traditional Japanese handyman. On the opposite end of the spectrum, he hangs out with a self-made millionaire in South Africa and jets off to Los Angeles to strut his stuff in a Hollywood fashion show.

Karl ends his journey with a look at differing attitudes to passing. He visits Ghana, where he shops for a customised coffin, before attending his first-ever funeral and the accompanying parade. He also meets members of a community in the Philippines who live and work with the deceased, is taught how to cry and deal with grief by a professional mourner in Taiwan, and returns to Britain where he creates a memorial.