Sherlock Holmes (1984)

Holmes and Watson are called in to deal with a blackmailer. A dazzling young lady is about to be married, and Charles Augustus Milverton, the slithery king of all blackmailers, has letters she wrote to another man. Watson is astonished when Milverton calls at Baker Street at the invitation of Holmes, who has a plan to thwart him. As ever, things are not quite as they appear to be.