From his hot air balloon flight over the zoo, sleuth Art sees something suspicious that later helps him solve a mystery.

As winner of talkback radio's Going Up competition, quiz whiz Art shares the prize of a hot air balloon flight with mates India and Mars Bar. It's India's birthday soon and Art hasn't bought a present. Mars Bar comes regardless.

The prize must be used at 4.30am next morning, but 9.am sharp on Wednesday is Mrs. Tasker's class visit to the Zoo. Luckily the flight path goes over the Zoo. The children are suspicious of passenger Mr. Brand who takes special photos. Luckily the balloon lands in time for the children's excursion. They meet the Cyclist, Shorty, and the Butterfly Expert and Kip the Zoo teacher. Art suspects all of them.

Later, in the zoo grounds, Art checks out the mysterious Butterfly House clue. After sleuthing around the Zoo, they solve the mystery. A smelly solution. Zoo Poo Cake.