Being the curmudgeon I am, I had some problems with a lot of the stories this month, since for me they missed the genre in the narrow way I was defining it. Spies may kill and be killed, but I wouldn't count stories which revolve around assassins, but with no actual spying involved, as spy stories; to my mind they're thrillers. I'll stay on the fence about whether James Bond as a not-very-secret secret agent fits the spy bill, but to reduce my curmudgeonish level slightly, it never worries me if Challenge entries are based on foreknowledge of other stories, though the preponderance of Bonds this month was rather overwhelming.
Anyhow, I've no time for a proper short list tonight, so just a quick shout out for scarpelius, Abernovo and Hugh, but my vote went to chrispenycate, for an imaginative and believable tale of spying.
Many secret ciphered thanks for the mentions/shortlistings nixie, Stable (thank you for the kind words), D3athw4lker, Phyrebrat and TDZ, and Top Secret microfilmed and exfiltrated thanks for the lovely votes johnnyjet and Joshua!