The Sign of Four

For years after her father's disappearance, Miss Mary Morstan has received one large, valuable pearl every year, anonymously. It is a strange kind of inheritance, and when an invitation finally arrives asking her to meet the giver, she does the sensible thing and takes the matter to Holmes. What he finds behind the pearls is a story nobody expected: clues that include a poison dart and a man with a wooden leg, and behind them an old soldier called Jonathan Small, still determined to punish the men who betrayed him and his friends over a hoard of stolen oriental treasure. The pearls, it turns out, were a debt being paid in instalments.

This is one of the long ones, a feature-length film, and it uses the time properly. The Sholto brothers, Thaddeus and Bartholomew, hold the key to the treasure's fate, and Ronald Lacey plays both parts with relish. The chase down the Thames ends with Tonga dead and Small in handcuffs, and the blowpipe is silenced for good.

Peter Hammond directed, from John Hawkesworth and Conan Doyle. Jenny Seagrove's Mary Morstan is clever and calm, which is why the story's other thread lands as well as it does: Watson falls for her, properly, and for once the romance is allowed to work. John Thaw, later famous as Morse, makes Jonathan Small a man you almost pity. Robin Hunter, Alf Joint, Kiran Shah, Derek Deadman and Rosalie Williams fill out the rest. There is a proper fog-bound chase, a death in a locked room, and a small man with a blowpipe who earns his place in the story.

The treasure story is greed and betrayal told on a big canvas, and the film leans into it without losing the small human details. And the ending, for Watson, is a rare happy one. That alone makes it worth a rewatch.