This scene SITUATES at the end of the story.
Sherlock Holmes and Doctor Watson ARE HAVING tea in the dinning room.
Holmes WEARS a dressing gown and OFFERS some biscuits to Doctor Watson.
Both LOOK relaxed and pleased.
In a few seconds, Holmes REVEALS how he FOUND OUT who IS the murderer.
Soon after, at the end of the conversation, he PRONOUNCES the very famous sentence"Elementary, my dear Watson"