Clinky Monkey catches a garden gnome breaking into the house, and Joe, Laurie and Theo understandably feel compelled to investigate - it's not every day you meet a talking gnome! They uncover The Great Gnome Robbery, masterminded by their strange neighbour, Mr Grimble, who is brainwashing gnomes with knobbly knees to infiltrate the houses of rich people and steal their valuables! But, as ever, the three boys have a cunning plan which will foil Grimble's plot, and uncover his strange secret.