From: ep. 3.3
Event: Sherlock becomes engaged in order to gain access to Charles Augustus Magnusson’s office. When he and John succeed in breaking in, he finds Magnusson being held at gunpoint by a woman whom he has wronged.
Reference: Holmes does this very thing in “The Adventure of Charles Augustus Milverton” (Magnusson is the updated version of Milverton, the Master Blackmailer). He and Watson break in and hide as they witness a blackmailing victim not only put Milverton at gunpoint, but shoot him dead. Things go slightly differently in ep. 3.3, but the basic build up to the event is the same. And as in 3.3, in the original story Watson is outraged and exasperated with Holmes for using the poor young woman in this way. In the original, Holmes declares he knows his fiancée has another suitor who will step in, and no more is said about it. In 3.3, a lovely Easter egg occurs with Janine raking in the cash from tabloids and retiring to a cottage on the Sussex Downs. With bees, no less (this of course is famously how original Holmes retires himself).