Three gentlemen not wholly useless to their country—a lawyer, a banker, and a cabinet minister—have suddenly fallen into a state of profound ennui. Each seeks to rediscover the comfort of their lives through 'the tonic of difficulty': adopting the nom de guerre of 'John Macnab', they take to poaching in the Highlands of Scotland, issuing challenges to three landowners and declaring their intention to take a salmon or a stag on their lands between specific dates. But can they overcome the challenges they have set themselves, and escape with their reputations intact?