When Steve Duno found a puppy -- flea-bitten and emaciated -- on a Californian roadside, he had no idea what he was letting himself in for. Lou, as he called the dog, was the offspring of marijuana farm guard dogs; a half-Rotweiller, half-Alsatian bundle of intelligence, loyalty, and mischief. Despite his traumatic beginnings, Lou went on to achieve great things, from foiling an armed robbery and fighting kidnappers, to comforting elderly war veterans and Alzheimer's patients. Most importantly, he inspired his owner to become a pet behaviourist, and worked with him to rehabilitate hundreds of aggressive dogs that would otherwise have been put to sleep. With a vocabulary of over 200 words, there was never any doubt that Lou was smart. But he was also funny, heroic, and, for 16 years, Steve's best friend and companion. This is their story.