Because I am aware that you have published several novels of the pulp variety--and have made rather a name for yourself among readers of those penny dreadfuls--and, most importantly, because I believe you do harbor some natural talent which requires the guiding hand of a competent and well-read editor--I have decided to dispense with formulae, and explain precisely why our distinguished house found your manuscript so lacking.
Understand, I am taking the time to do so in the hopes that you will profit from the critique, improve your work, and find publication with a suitable firm.
Now then--the matter of your protagonist. My dear young man, you violate a prime principal of the mystery right from the start of your labor. You simply cannot have such an unlikable fellow lead the reader through the byzantine plot--more on that later. With the possible exception of Sherlock Holmes, all protagonists must be likable. Make them blind priests, make them Belgian detectives, make them elderly ladies in small English villages, but please--make them likable.
The fact that your "hero" indulges in illicit sexual activity precludes him from being a gentleman at all ... and I suggest you redefine him as more fitting for polite society. If you need inspiration, I suggest Philo Vance or Lord Peter Wimsey. The latter has even been known to utter an occasional "damn" or two ... you may find him a helpful model.
That brings me to your second major problem. The woman is all wrong. Her motivations are unfeminine, and she is, simply put, sordid. You make it clear that your protagonist is attracted to her, despite her past and her criminal deeds. This is wrong as well. I suggest you rewrite her to be more sympathetic (likable, remember!) and arrange the plot so that the two of them unite. Perhaps you can resurrect the dead partner (who wasn't really dead, but crawled for help), and he can bless their union at the end. Something warming and conclusive, but not this open-ended nonsense.
Characters in general are also all wrong. You are clearly referencing taboo subjects: homosexuality, for one. No one is likable at all, except, perhaps, the secretary, and I am sure she is the sort of woman who is no better than she has to be. If you know what I mean, and I'm sure you do.
Setting--no, no, no. Setting is everything. And if it is not set in a penthouse or an English estate or a lonely cottage on a moor, you are simply not going to attract mystery readers. San Francisco is a lovely city, I am sure ... I haven't visited it myself, though I understand they have mainly recovered from that terrible earthquake. But its reputation is still, shall we say, not exactly Mayfair. Again, just too sordid--especially with your unlikable protagonist (see above).
The plot was convoluted and too many things happened too quickly. You dropped us in the middle of things, sir--where is the set-up? Where is your backstory on your protagonist's partner? Time, sir, time--you need more words and you need to slow down and tidy up.
Finally, my dear sir, there is your style. I understand that Mr. Hemingway has exerted a strong pull on many an author of late, but truly--you do yourself and the mystery field a disservice by such staccato phrasing. Why, your prose is barely comprehensible! Where are the long, detailed descriptions of scenery and breakfast food? Where is the expository background? Virtually the only item you think worthy of attention is a story told by the hero to his paramour ... a story that makes no sense, and apparently about a man who was hit on the head and abandoned his wife. I ask you, is this the stuff of Christie and Sayers and S.S. Van Dine?
One last suggestion before I close. Really, sir--a Maltese Falcon? Surely you can do better than such outrageous nonsense. Poe was undoubtedly on an opium high when he wrote the Raven, and I half-way suspected you were, too, to invent such a nonsensical creature.
Mr. Hammett--you are a writer of limited gifts, at best. If you wish to succeed in the mystery genre, I suggest you follow my suggestions on how to make your book more acceptable for publication. I am thinking not just of the present, but of the future.
Trust me, dear sir--this "hard-boiled" craze you seem to have ignited will soon become a rotten egg.
Editor in Chief
Editor in Chief