This American mystery novel is from 1911, and is therefore coaeval with the work of Anna Katherine Green. The detective most invoked throughout, however, is Sherlock Holmes, clearly the model for Fleming Stone, whose particularly acute ability to deduce unbelievable amounts of evidence from physical objects is clearly a Holmes reference, if not actually intended as mild satire. What's somewhat interesting about "The Gold Bag" is the absence of said Fleming Stone from the proceedings, except at the very beginning and the very end. The bulk of the investigation falls on one Burroughs, who tells the tale, and whose work serves chiefly to eliminate the various red herring suspects. He also, unfortunately, develops a passion for the principal female, and though Wells had a go at suggesting it made Burroughs a less reliable investigator, I don't think in fact that unwanted plot point served the novel in any substantial way.
I will not be committing a spoiler offence, I shouldn't think, in noting that the eventually-disclosed motive for the murder is financial. And there were enough clues on the table in the deportment of the murderer that I at least had that person firmly on my suspect list well before Fleming Stone came in to read the evidence and make the dramatic accusation.
This is a high society novel of the American type, in that while no-one titled is involved, the principal players are all monied white Anglo-Saxons, and the servant characters are risible caricatures of non-Anglo-Saxon national characteristics, in this case French and Dutch (or possibly German; Wells makes reference to both).
The language is unexceptionable and there is clearly a good mind behind this book but it's not first-class detective fiction, even allowing for the fact that it's pre-Golden Age. Looking Wells up, she appears to have been beyond prolific in her writing, and married to a major publisher, which may well mean that she was subject to less rigorous editing than a contemporary might have been.