Amy and Becky, identical 10-year-old twins, find that their grandpa, a retired chemist, had accidentally discovered a formula which will make things disappear as well as another formula that will reverse the process. When grandpa is away, they apply the potion on themselves, hoping to have fun by being invisible while they play a trick on their friends. Dogs bark at the invisible girls and a woman shrieks when she doesn't see them but hears their voices. Their greatest adventure occurs when they find their friends' house is being burglarized, and the have fun scaring the crooks away. But after they return, they apply the formula which was supposed to make them visible again. Oh no! it doesn't seem to work. What will they do? Will they miss out on the rest of their lives because of this? This is an unusual adventure story for boys as well as girls, and it will keep them reading from cover to cover.