Mr. Magoo is reading a "whodunnit" novel when his nephew, Waldo, comes in saying he has totalled Magoo's car and needs $100 to buy his uncle a new one. Magoo gives him some money but warns Waldo not to "go outside the law" while obtaining the rest. Magoo becomes suspicious and decides to track down Waldo for his own good donning a phoney beard disguise. He sees Waldo as part of a lineup (for a radio quiz program) and "rescues" Waldo from what he thought was a police lineup. Soon, Magoo becomes more and more convinced there's a mystery to be solved and a thief to be apprehended particularly after he and Waldo enter an abandoned warehouse.