After suddenly losing his parents, Yu-Du falls into grief and loneliness. Determined to find a new direction in life, he sets out on a journey.

Along the way, Yu-Du stumbles upon a city entirely inhabited by animals — dressed in everyday clothes, each with their own jobs, living in perfect order. Mistaken for a monkey, Yu-Du befriends a little cat named Barkley and his band of companions.

Barkley takes Yu-Du to the city's grand festival, where Yu-Du discovers that the city's ruler is the only other human besides himself. What is the conspiracy hidden behind this city? To uncover all the secrets and lies, Yu-Du and Barkley's adventure is just beginning.