This was a great ending to a consistently excellent series. Somehow Sarah and I had read the first (2?) entries years ago but didn't get to this one (maybe it didn't exist?). Nevertheless, I enjoyed this quite a bit and I think it's a great contribution to the community-of-weirdos-take-care-of-your-people genre that middle-grade books often work in. Hilary is a really good protagonist, and Carlson does a lot of work with dramatic irony with her, making sure the reader knows what's going on even if Hilary doesn't or won't say it.
The portrayal of pirates in these books is fascinating. I kept trying to lay real-life groups on top of the pirates, but there isn't a perfect analogy. Deeply invested in protocols and rules while at the same time insisting on the necessity to break protocols and rules, ostensibly criminals but understood to be an important piece of the cultural system, as well as talking a big game of violence, but mostly being gentle doofuses that are confused when they might have to actually hurt someone, the pirate system is probably the most original genre contribution in the books.
High recommendations for the whole series.