Simon Templar is the Saint - daring, dazzling, and just a little disreputable. On the side of the law, but standing outside it, he dispenses his own brand of justice one criminal at a time. When the Saint and Patricia Holm stumble upon a government test of a weapon of mass destruction, they realise they've seen something that must be kept away from the wrong hands. But the Saint's nemesis Rayt Marius is already nearby... There is only one way to stop Marius from using the weapon to start a war - kidnapping the scientist who built it. The plot comes to a climax on the banks of the River Thames, and not everyone will survive.