The hardboiled detective of Radio Noir is often out on his own, with nothing but his wits, his loyalty to his client, and confidence in his own abilities to bring him to safety. The criminals he pursues will have no hesitation to plug him full of lead if he gets too close to them, and the cops see him as a parasite that should be locked up to get him out of their way.
A Spy has many of the elements of a hardboiled detective. His client is usually his government, but the fictional Spy seems to be attracted to the danger of his assignments as often as he is loyal to his country. The spy usually has the full support of his agency to help insure his safety. He is so close to the enemy though, that even if the agency tried to help they would likely compromise the spy’s safety through anonymity. The government is playing for bigger stakes, and ultimately the Spy is expendable; to everyone but the Spy himself, of course.
It isn’t uncommon for a Hardboiled Private Eye to lose his head over a Dame, and the Red Blooded Spy has the same urges. The Detective may be working for the girl, to defend her or bring justice to her cause, but more often she is part of a Honey-trap set by the bad-guys. Honey-traps are common pitfalls for Spies as well. Sometimes the Spy can bring the girl over to the side of right, but if she is as dedicated to her cause as the spy is his, then she is likely evil beyond redemption.
I was a Communist for the F.B.I. blends the elements of the Radio Noir Hard Boiled Detective and the Spy Thriller, but though he is working for a Police Organization, The FBI, he is more a Spy than a Cop or Detective. Matt Cvetic (played by Dana Andrews) is in deep cover with the Communist Party of the USA. The show makes no secret that the CPUSA is a front for the Soviet agenda. Any miss-step will give away his identity and cost him his life. He cannot even tell his family about his activities, so he is completely on his own. The only thing that keeps Cvetic going is the knowledge that the enemy intends so much damage to the USA.