This does sound similar to the story I'm currently working on, as fufaraw mentioned. It is a fill for an spnkink_meme posting. I haven't read Hostage yet, only so I don't ball up my story and toss it in the wastebasket.

It is an AU where a small percentage of men are carriers, though, and not a/b/o dynamics. It is set in 1853 and takes place in Qatar, with flashbacks to their time in London and Somerset.