Ten-year-old Emily has always felt like an outsider, bullied at school and estranged from her distant parents, since the birth of her brother. Until she finds and adopts a small red puppy at the marina where she likes to hang out. Naming him Clifford, Emily instantly bonds with him, and it seems Clifford is rapidly growing, genetically testing as a result of a mysterious mutation. When a powerful biotechnology company takes an interest in Clifford, Emily goes on the run with the help of her Uncle Casey across New York City, in an effort to keep her beloved friend safe. Clifford's journey and the lessons he teaches along the way warm hearts and free those who are misunderstood.