Widower Tom, on the recent passing of his wife Mary, uses his free bus pass to travel the length of Britain from John O'Groats in Caithness to Land's End in Cornwall, their shared birthplace, using only local buses. It's an incident-fuelled nostalgia trip and his encounters with local people make him a media phenomenon. Tom is totally unaware and to his surprise on arrival at Land’s End he’s greeted as a celebrity.
In the teeming, multicultural metropolis of modern-day London, a seemingly straightforward missing-person case launches a down-at-heel private eye into a dangerous world of religious fanaticism and political intrigue.
Based on the real life story of legendary cryptanalyst Alan Turing, the film portrays the nail-biting race against time by Turing and his brilliant team of code-breakers at Britain's top-secret Government Code and Cypher School at Bletchley Park, during the darkest days of World War II.