In the movie, the blackmailer is revealed to be a master of disguise who goes by the name Charles Augustus Milverton. Holmes and Watson's investigation leads them to a wealthy businessman who has been blackmailing various individuals for years, using their secrets to extort money and favors from them.
In order to stop Milverton, Holmes concocts a plan to steal incriminating letters that the blackmailer is holding over the head of a young woman named Lady Eva Blackwell. The plan involves Holmes posing as a wealthy American seeking to purchase the letters, with Watson acting as his manservant.
Things take a dramatic turn when Holmes becomes romantically involved with Lady Eva, leading to a tense showdown between the detective and Milverton.
The movie features the classic Holmes/Watson dynamic, with Jeremy Brett and Edward Hardwicke reprising their roles from the popular Granada Television series "Sherlock Holmes." The film was well-received by both fans of the series and newcomers to the world of Sherlock Holmes.