Trueman Bradley visits London and sets up shop on Baker Street, in the hopes of becoming the next Sherlock Holmes. Using hints he has derived from the original Sherlock stories, Trueman uncovers the mysterious methods of "The Great Detective" and uses them to solve the mystery of how his grandfather acquired his fortune, as well as helping Scotland Yard to capture a notorious cat burglar.

With the help of a few new friends, Trueman learns the value of deduction, imagination and instinct in detective work, and proves that he has what it takes to become "The Next Great Detective."