"Scooby Dog" is the first big-screen animated adventure feature of Scooby Dog, which tells the unknown origin story of Scooby Dog and the most amazing secret case in the history of mysterious companies. Scooby Dog depicts the first encounter between Scooby and his lifelong friend Shakie, and how they formed a world-famous mystery company with teenage detectives Fred, Velma and Daphne. Today, mystery companies have solved hundreds of mysteries and taken countless adventures, but Scooby and his companions have found that they are facing one of the most thrilling and challenging mysteries of all time: a plot to release the ghost dog Cerberus into the world. While they were desperately trying to stop this global catastrophe, they also discovered Scooby's secret story and his unimaginably mysterious fate.