Claire Guest was walking her dogs when Daisy, a fox red Labrador, nudged her breast insistently and stared up into her face with her big brown eyes. Sensing something was wrong, Claire visited her GP and soon found out she had a very deep—and difficult to diagnose—form of breast cancer. Daisy had saved her life, simply by smelling her cancer. With her scientific background and deep love of dogs, Claire intuited that Daisy and her canine pals could save many more lives, and set up the charity Medical Detection Dogs. Though faced with many challenges, Claire and her dogs have proven to be a remarkable asset to cancer detection, and have changed the lives of many seriously ill people and their families. This is the story of how our relationship with dogs can unleash life-saving talents, changing not only the medical world, but our own lives too.