A famed blue ruby is stolen in such an elaborate fashion that the only suspect is Professor Moriarty. Sherlock Holmes is tasked with retrieving the gem, and along the way he must steer a young pick‑pocket toward a better path. In the second part, Moriarty sets his sights even higher, absconding with a top‑secret submarine from the Navy. What he intends to use it for remains unknown, but Holmes is once again on the trail.