The Baker Street Irregulars are on the case, assisting the master detective Sherlock Holmes with a most compelling mystery. With the help of the BSI, Holmes has set an elaborate trap to capture Professor Moriarty and dismantle his crime organization, at last! But Moriarty has his own plans. In their latest adventure, the Irregulars face the greatest challenge of their careers. The quest will take them, for the first time, out of England and on a thrilling chase through continental Europe. Will Holmes and the Irregulars succeed? Or will they fall prey to the most dangerous man in all of England?