Competition in the taxi trade is at a record high. Each month, for every new driver joining the elite club as a black cab driver, 16 new minicabs, including the likes of Uber, hit London's roads. This programme goes behind the scenes of one of the hardest exams in the world; the one that all the black cab drivers in the capital must take: The Knowledge of London. Candidates must memorise the capital's 25,000 streets and traffic restrictions, and its ever-changing 100,000 points of interest. The volume and detail of information is compared to doing a degree in law or medicine. It takes an average of four years of grit and determination to pass, and the dropout rate is 70%. This programme follows a single mum, a Kosovan immigrant and a bus driver - ordinary people doing something extraordinary. When it comes to our increasing dependence on technology, The Knowledge reveals the power of our brains when they're pushed to the limit.