In this installment, Tim Diamond, the world's worst private detective, and his younger brother Nick, a brilliant 13-year-old, find themselves embroiled in a dangerous adventure. Tim, broke and desperate, accepts a large sum of money from a mysterious stranger for his overcoat. Soon after, the stranger is shot, and the brothers are thrust into a perilous situation involving international intrigue and a plot to assassinate a foreign dignitary. With Nick's intellect and Tim's unintentional luck, they navigate a series of misadventures to uncover the truth.