When a supposedly uncrackable bank vault called 'The Leviathan' is breached for the second time, Sherlock is called in to figure out what went wrong. When the vault was breached for the first time, the heist was committed by a once-in-a-lifetime assembly of world class criminals. Because they went to jail for the crime, the vault company can't imagine how anyone else got in. When Sherlock learns that not even he can break into The Leviathan, he realizes that the second group of criminals must somehow be connected to the first.