Twin Killing is a history of a serial killer. Robert David Smalley has been murdering twins and their mothers for over forty years. Three times in California, once in Washington and now in Texas. Getting old and worried that he can not continue, he turns himself in to the Dallas Police Department. He refuses to talk to the DPD or FBI. He will only talk with Wayne Mitchell, a retired detective from Oakland, California. Mitchell's first murder investigation was Smalley's first Twin Killing.