The Mazarin Stone

The Mazarin Stone is a famous jewel with a criminal career, and this episode finds it at the centre of its latest adventure. There is only one problem. Holmes is not there. The great detective has gone to the Highlands, which is a bit like the goalkeeper missing the cup final, and the case is left to Mycroft, Watson, and the considerable resources of Baker Street.

The theft of the diamond has Mycroft investigating, and Watson has picked up a peculiar smell. Someone is offering five million dollars to a former professor if he can find a third man named Garrideb. Five million dollars for finding a man with a particular surname smells like a trap, and Watson, who is often underestimated by criminals, can see it from across the street.

The episode borrows from two Conan Doyle stories at once, which is a bit like getting two helpings of pudding. Count Sylvius has his eye on the stone, Lord Cantlemere frets about the nation's honour, Inspector Bradstreet does the legwork, and the Garridebs sit at the centre of a scheme that has nothing to do with family reunions. And Gavan O'Herlihy plays both John Garrideb and James Winter, which is the sort of doubling that tells a sharp viewer everything.

Gary Hopkins wrote it, Peter Hammond directed. Jon Finch is Count Sylvius, James Villiers is Lord Cantlemere, Denis Lill is Inspector Bradstreet, Phyllis Calvert and Barbara Hicks are Agnes and Emily Garrideb. Charles Gray is Mycroft, holding the fort with Edward Hardwicke's Watson, and Rosalie Williams is Mrs Hudson. Jeremy Brett appears as Holmes, eventually, and the episode is all the better for making us wait for him.

The Mazarin Stone is a romp, and it knows it. Even with the master detective offstage, Baker Street runs on the same old certainties. The criminals will overreach, and the trap will spring. The jewel goes home before the end credits.