OP says the books are written, so good on them, but I just wanted to say that I worked public safety, and yes, there are hard and fast rules against such things, and yes, they are broken all the damn time. When you're in that job (I was 9-1-1, but police officers, firefighters, and medics are in the same boat) every person you interact with professionally is having the worst day of their lives. Even if it's only a giving a speeding ticket, you've just wrecked their whole day, if not week, and that wears on you. A lot. I worked midnight shift, and we used to go out for breakfast together, the whole shift, at the only restaurant that served beer at eight in the morning. The servers learned two things: Put us at a table in the corner, away from the other customers' earshot, and we tipped very well. The first was because we'd laugh about dead babies and decapitations, not because they were funny but because one of us had just had to deal with them and if you couldn't laugh you'd make a right turn out the door instead of a left into the dispatch center after roll call and never come back. That happened once. The dispatcher just couldn't deal with another day of it and quit rather than plug in. The second, the tipping, was an acknowledgement of the waitstaff dealing with the first. So anyway, yup, the departments all have rules against dating coworkers and especially superiors, but they are the only people who know what you just went through, and if two of you end up in the quiet room together, well, you won't be the first.
Also note people in similar professions, a lot of cops date emergency room nurses, both because they know what it's like to see nasty shit, and because the er is a good place for a cop to hang out, it's warm, you're reasonably safe, there's coffee, and pretty women.
Similar professions, no problem. Been there, done that. Direct co-worker or boss? Big problem. The phrase "Never shit where you eat" was always a favorite phrase among my coworkers.
The detective inspector is the female -- and the superior. In any case, she holds the position for quite a while (and he, his -- he gets a transfer from another city, rather than a promotion) before the books begin. However, your knowledge is very helpful for future reference. Well, it's still interesting to know what people think . Especially because I hope I'll write more stories involving cops (and doctors and nurses, actually) in the future.