Sherlock Holmes, Dr. Watson, Irene Adler and Inspector Lestrade must solve thirty of the most complex and intriguing cases ever to test their abilities. Each investigator thinks he or she is best able to find solutions, so they decide to turn each mystery into a friendly competition of their skills.
The famous four meet at 221 B Baker Street, the address of Holmes and Watson. From there, they travel the streets and alleys of London, gathering clues and trying to outsmart each other. Explorers use secret tunnels for quick access to other parts of the city. They acquire badges from Scotland Yard to lock the doors of buildings containing valuable evidence. Of course, locked detectives can find the keys at the Locksmith.
The detectives are armed with secret codes, allowing them to obtain exclusive information from fifteen locations throughout the city. Working to solve the crime, they each try to break the others' codes in order to have access to more clues with less work. They can also change their own codes to throw others off the track.