Stories that shouldn't be written

How do you get your muse to stop prodding you about a story idea that shouldn't be told? Every so often my writing goes to a dark place, but I've got a story concept stuck in my head that's unwriteable, and I can't figure out how to make my subconscious shut up about it.

Warning! What folllows is a description of an offensive story.

Here's the concept: it's sort of a noir tale told from the point of view of a police detective, who one day has this gorgeous woman come in. she's dressed to the nines, looks to be somewhere in her late twenties to early thirties, but with society dames like that you can never tell what with facelifts and botox and everything. She says she has information about a kidnapping. The detective looks up the case and it's about a four-year-old boy who was abducted ten years ago. She explains that she's pretty sure she is that boy.

So far, it seems like a pretty good hook, which is why I'm having trouble dispelling the concept.

However the meat of the story is that the boy was abducted by a sick pedophile who gave him hormones to keep him sexy, but when he started getting too girlish he gave her growth hormones to prematurely age her, and had her pretend to be his wife. But he really wasn't into adult women, so he shows up one day with a baby boy for her to raise, and the baby grows to be almost old enough for him to start playing with, and that's when she goes to the cop.

It's the details that make it unwriteable. To really convey what she went through, the story would come too close to being child abuse-porn. Plus as a noir there has to be a hint of romance between the cop and the damsel, but she's really underage so he has to suppress it - I could make her older, but it loses the aspect of a child in an adult body trying to cope. The writeable part of the story would deal with her trying to reconnect with her family while losing her child, and the toddler being taken away from the only mommy he knows, but it doesn't seem like that can really be described without showing the reasons why she feels the way she does.