The Caithness coast. Winter 1745. Rebellion year. A half-mad earl witnesses a murder. But seeing the appalling decision the killer had taken leads him to invent his game of life The Prisoner s Dilemma and he writes to his old friend, David Hume, inviting him to his ancient stronghold to explore its meaning. Hume is only too pleased to go. He has just met Adam Smith and the two of them have disagreed about man s instinct for survival - and how compassion can exist in a world driven by self-interest. But before Hume s discussions with the earl can begin, two strangers arrive from Prussia who...