From: ep. 2.2
Event: Dr. Frankland runs away from his pursuers into the Great Grimpen Mine Field, and there meets his death.
Reference: In the novel from which the ep is adapted, The Hound of the Baskervilles, it’s not Frankland but Stapleton who is the culprit. He flees from the pursuit of Watson, Holmes, and Baskerville through the Great Grimpen Mire, and it’s intimated he has sunk into the muck and died.