The Final Problem

The Mona Lisa is stolen from the Louvre, and the French government, in a state that can be imagined, sends for Sherlock Holmes. He takes one look at the job and decides it is no ordinary thief at work. The hand behind it is Professor Moriarty, his old enemy, and Moriarty means to sell Leonardo's masterpiece rather than return it. Holmes spoils the sale, and then he has to survive the consequences, because a humiliated Moriarty is a dangerous one.

The chase runs across Europe and ends in Switzerland, above the Reichenbach Falls. The confrontation there is the famous one, the fight at the waterfall from which, the series would have us believe, nobody climbs back. Holmes and Watson face it together, and the season closes with both of them apparently lost, which is exactly the cliff the canon left hanging.

Eric Porter makes Moriarty properly terrifying, courteous and cold, a worthy end for the series's great adversary. Jeremy Brett's Holmes and David Burke's Watson carry the weight of the thing, and Rosalie Williams, Olivier Pierre, Claude Le Saché, Michael Goldie, Robert Henderson, Paul Sirr and Jim Dunk fill the edges.

The episode is something of a curiosity, an original storyline that invents the Mona Lisa theft and brings Moriarty to the screen alive in order to reach the canonical ending Conan Doyle wrote. John Hawkesworth's script, with Arthur Conan Doyle's name alongside, builds the bridge from the stories to the famous fall. Alan Grint directs, and the series ends on its darkest note yet.

It is a bold way to close a season. Fans who know the canon will be waiting for the return, and the production has the confidence to let the ending stand on its own, dark and final. But whether it stays final is another matter, and that is a question for the next series.