In 1950s London, Tom Knelston is charismatic, charming, with a passion for politics and reform. He is a man with ambition―and someone to watch. His wife Alice, a former nurse, shares his ideals. It seems they are the perfect match. Then, out of the blue, Tom meets an old childhood acquaintance, the beautiful and unhappily married Diana Southcott, a fashion model. In many ways, she is everything Tom fights against, but she is also irresistible and so, flirting with danger, they embark on an affair that is potentially damaging to both. And when his child becomes ill, Tom is forced to make decisions about his principles, his career, his marriage, and, most of all, his love for his child.