Doctor Proctor's Fart Powder (Paperback, Reprint ed.)

Nilly is new to the neighborhood, but is quick to make friends: Doctor Proctor, an eccentric professor; and Lisa, who is teased by the twin terrors Truls and Trym. Nilly and Lisa help Doctor Proctor develop his latest invention, a powder that makes you fart. The powder makes Nilly and Lisa VERY popular at school when they sell it for 50c a bag. And they get revenge on Truls and Trym by giving them an extra strength dose of fart powder that shoots them up into a tree. All is good farty fun. Until someone steals the industrial-strength fart powder -- that was supposed to make Doctor Proctor famous -- to use for evil purposes...