“The Problem” is Chapter 3 of Arthur Conan Doyle’s “The Hound of the Baskervilles”. Dr. Mortimer, a friend of Sir Charles Baskerville, pays a visit to Sherlock Holmes at 221 B Baker Street. He offers Holmes with a document containing the Baskerville family’s history stretching back to the 17th century.

The myth mentions a curse on the Baskerville family, in which Sir Charles’ ancestor was killed by a mystery hound. The document also recounts a recent sighting of the same hound at Sir Charles’ manor in Dartmoor.

Holmes is intrigued by the story and agrees to assist Mortimer. He interviews him further about the case’s details, such as the exact location of the sighting, the size and appearance of the hound, and any other unusual events that may be related to the case.

Mortimer informs them that Sir Henry Baskerville, the last of the Baskervilles and Sir Charles’ successor, is scheduled to arrive in London the next day. Holmes advises that Mortimer bring Sir Henry to meet him before departing for Dartmoor, and Mortimer agrees.

Holmes also wants Watson to follow Sir Henry to Dartmoor and report back to him on any observations. Watson agrees, and the two leave for Devonshire the next day.