As a lifelong fan of London, Mark Mason embarks on a mission to 'conquer' the capital once and for all. The only way to truly discover a city, they say, is on foot. Taking this to extremes, Mark sets out to walk the entire length of the London Underground - overground - passing every station on the way.

Over the course of several hundred miles, he comes to understand a sprawling metropolis that never ceases to surprise. In a story packed with historical trivia, personal musings and eavesdropped conversations, Mark learns how to get the best gossip in a City pub, how the Ritz made its female guests feel good about themselves, and why the Bank of England won't let you join the M11 northbound at Junction 5. He has an East End cup of tea with the Krays' official biographer, discovers what cabbies mean by 'on the cotton', and meets the Archers star who was the voice of 'Mind the Gap'.

On a broader level, Mark contemplates London's contradictions as well as its charms. He gains insights into our fascination with maps and sees how walking changes our view of the world. Above all, in this love letter to a complicated friend, he celebrates the sights, sounds and soul of the greatest city on earth.