Ever since the Johnsons took him in, Cosmo has led a normal life. Playing fetch and chasing Chloe, the neighbor's cat, have kept him quite busy. But one day, Cosmo begins thinking about his happiness. Is he truly as happy as he could be? And so, Cosmo begins a quest to become the happiest dog ever! At the end of his adventure, will Cosmo find that he is happier than when he started, or will he discover that his true happiness was right in front of him all along?