Sherlock Holmes is at it again in “The Adventure of the Mazarin Stone.”Dr. Watson arrives at 221B Baker Street to find his old friend and colleague keen on a case. Holmes has taken it upon himself to find the missing Crown diamond, the Mazarin stone, which has been stolen by swarthy big-game hunter Count Negretto Sylvius. When the count pays Holmes a visit, the brilliant detective must rely on his cleverness to learn the jewel’s location and wrap up the case.