Mystery and adventure follow the BSI as they embark on their most important case yet, when Holmes's associate, Dr. Watson, is abducted!

Sherlock Holmes's trusted assistants, a band of loyal street urchins called the Baker Street Irregulars, are back for their most puzzling mystery yet, in a case that involves murder, abduction, and the hunt for a lost treasure. As Holmes and the BSI begin their investigations into a gruesome murder, all at once the detectives find themselves in danger. When a personal associate of the master detective disappears, Ozzie, Wiggins, and the gang know that they must uncover the truth - and quickly! Yet there is deception within their ranks. Who is a friend? Who is a traitor? Who can they trust?