While to a large extent, a book would have to be really good to make much of an impression after reading Iron and Magic, this...
I really hate the v. basic plot of h is in danger and it takes H forEVER to figure out who the villain is (who often is a relative with some pointless and stupid grudge). Occasionally it's the H but it still takes forever, and still seems pointless.
In this case, it's further hampered by it taking a month for it to even occur to them that *maybe* there were secret passages (in a castle? Of course there are. D'oh). And after all that, and them finally figuring out who, the who in question makes one last attempt, though I fail to understand why. Seems like the wisest course of action would have been to run.
The H/h pairing? No problems with that. Really, this one would have done just fine focusing on their relationship development..but then again, so would the rest of the series. Unfortunately (and this isn't necessarily an issue with this author; it's the genre in general), we don't get that.