It seems as though most successful authors hit a point at which either they have no more ideas, they no longer have time to do the job well, or they just don't care any more. "Hell Gate" is the clearest indication yet that Fairstein has hit this point. As others have mentioned, there are two plot threads. One involves a Congressman whose political career may be derailed by a girlfriend (and yes, of course he's married) claiming that he tried to kill her. This hardly seems like Alex Cooper's territory. The other plot thread involves the shipwreck of a ship carrying three hundred passengers who were intended to be smuggled into the US and sold as slaves. That, at least, is within Cooper's bailiwick, although she's in the mix a little bit early -- the passengers haven't even been identified before she's interviewing them.
Unfortunately, the human trafficking plot takes a back seat to the political maneuverings, as Cooper and her cop friends more or less stumble over clues to what is really going on with the Congressman's girlfriend, and how it relates to the trafficking operation. In this volume, it's a real stretch to connect the story with a bit of New York history, and the connection of the crimes with Gracie and two other federal-era mansions is tenuous. As noted by another reader, the usual history lessons are not well integrated into the story (although, unlike that reader, I thought they were more interesting than the political plots) and really stick out.
Romance has never been Fairstein's forte. That's OK -- she should just give Cooper a boyfriend, stick him in occasionally, and forget about it. We can imagine most of the relationship. This, however, does not seem to be the direction in which she (Fairstein) is headed. Instead, she seems to be heading toward a Mike/Alex romance. DON'T DO IT, Ms. Fairstein! I, for one, would find it highly unbelievable. The fact is, I dislike Mike. I don't think it's intentional on Fairstein's part, but I find Mike's so-called "banter" to be a lot like the teasing of adolescents -- meant to seem like teasing while carrying a real bite. The things he says are often mean, and certainly unprofessional and inappropriate in a business context. Another way of looking at it is that he is trying to "claim" her in front of other parties by saying things that suggest that they are intimate (although not necessarily in a sexual way). I hate it. Alex should hate it and call him on it. Certainly no romance should happen unless he grows up a LOT.
In short, read this book if you like Cooper, but don't expect too much from it.