Topper and Lexington are curious cats, but they've always obeyed their mother's one rule: never leave the yard. But when the full moon vanishes from the night sky, leaving behind something strange and red in its place, Topper and Lexington leave the safety of their yard to find the missing moon somewhere in the dark. Wonderful creatures exist outside their yard, including owls, dolphins, and even mermaids, but scary creatures are out there, too. Can Topper and Lexington find the missing moon-and their way back home?