What have the Black Hand Gang done? Have they kidnapped Wills, a brilliant young inventor? Where is he? Where have they taken him?
No one knows where Wills has gone - and his best friends, the twins Harry and Camilla - are very worried. Last time they saw him, Wills was with the Black Hand Gang - and he looked extremely unhappy! Luckily, Wills has left the twins lots of clues to follow - maybe they'll find him soon. You can solve the mystery; you can find Wills. You'll discover his fantastic inventions too!