In 1970s Hong Kong, Tiger, a secondary school student at Resettlement Area Rooftop Primary School, spends more time having fun than studying for his classes. His only ambition is to become a superhero, so he makes himself a cat mask. On report card day, he wants to show his mum his academic progress, but his report card is mistakenly taken by someone else. With no other choice to avoid punishment from his mum, he sets out to retrieve it and ventures into Kowloon Walled City, a notorious shantytown where no rules apply except those of the mafia. All kinds of illicit businesses flourish: gaming rooms, opium dens, and undercover trading. There, he meets a new friend named Dragon, who offers to help. Together, they must confront their fears and recover the lost report card!