Did you notice that, in The Hound of the Baskervilles, neither Holmes nor Watson is a member of any official police force? Obviously, they're committed to solving crimes and making Dartmoor a safer place for future Baskervilles. But they don't actually have a legal obligation to deal with every crime that they see.
So when the Barrymores finally confess that they have been sheltering an escaped convict out on the moors, Watson doesn't have to arrest them. Holmes and Watson are free to use their own judgment about the right thing to do on a case-by-case basis—whether Scotland Yard agrees with them or not.
Questions About Justice and Judgment
What's the difference between justice and law in the The Hound of the Baskervilles? Which characters seem most closely associated with which concept?
Are there any characters in The Hound of the Baskervilles who escape justice, in your view? How or why?
When does Watson criticize Holmes' judgment? What flaws does the book show us in Holmes' decision-making?
Chew on This
Mr. Frankland's nuisance lawsuits and the relative unimportance of policeman Lestrade as a character all indicate that The Hound of the Baskervilles values individual moral judgment over the authority of official institutions of the law.
Holmes might be less motivated by a wish for justice than by the challenge of problem-solving.