Sigerson Holmes has something to prove as the lesser-known brother of famed detective Sherlock Holmes. When Sherlock and his assistant, Dr. Watson, are dispatched to Europe on assignment, Sigerson takes the opportunity to prove his mettle as a sleuth. With the aide of bug-eyed Orville Sacker and aspiring opera singer Jenny Hill ), Sigerson attempts to crack the case of missing government documents presumed stolen by professor Moriarty .