Protector of the Small: Lady Knight, Book 4.

Finishing off the Protector of the Small quartet, LADY KNIGHT is an excellent end to a good series. It's the story of Kel's first big assignment as a knight: running Haven, a refugee camp near the border with Scanra. In her Ordeal of knighthood she was given a task by the Chamber, and chafes at the feeling that running the camp is holding her back from going after the man killing children and turning them into strange metal monsters. There are new storylines related to her time running Haven, and her care of Tobe, a boy with horse magic. I don't think anything is both introduced and resolved here, since the biggest rescue relates to the task the Chamber set her in SQUIRE. Technically a great many characters' storylines are "resolved" through death, but those who are met and then later killed are nearly as many as those whose first mention on the page is when Kel finds their bodies. 

As the final book in the quartet it leaves open the idea that Kel and her comrades will have further deeds when this is done, and it settles what she'll do after Haven. It resolves the magical threat posed by the killing machines, and gives an idea of what her friends will do next. It teases a few things that could happen later for secondary characters, but these won't necessarily show up in future Tortall stories.

Kel is still the narrator, with the exception of a brief section from someone else's perspective. She definitely sounds older than the first two books, and her characterization in LADY KNIGHT is consistent with the end of SQUIRE. Other than the fact that Kel was set a task before the book begins, this is self contained enough that it could mostly make sense if someone read it without any of the other books. It covers only a few months, rather than years, and focuses on events within a small area once it gets going. The ending will definitely be more satisfying for someone who at least read SQUIRE, but there's still a lot to love for any readers who try starting here (especially if they're familiar with Tortall as a setting from other series).

Kel has grown up a lot but is very aware of how much she still has to learn. She has a lot of strong relationships which get a chance to pay off here. She's not hanging out with people as much, since her duties and her organization of the refugees take the narrative place that training filled in the earlier books. However, Neal, Dom, and Owen have a strong presence, and I'm fairly confident that this has more of Merric than the rest of the series combined. The animals play an even bigger role this time, made possible by some help from Daine.

The worldbuilding focuses on the logistics of running Haven, as Kel begins having to to many things herself and gradually gets infrastructural support and clerks to make some aspects easier. There's some detail about the war, but as the fourth book of a quartet set in a world already filled with stories, it doesn't pause to explain quite as many things as the earlier books did. There's still enough to make the relevant things make sense, and it works overall.

The plot is the most focused of the quartet. Kel has two main things she needs to accomplish, and she works on running Haven until she gets the information she needs to act on the directions from the Chamber. I enjoyed the process of turning Haven into a defensible position filled with confident civilians who know how to defend themselves. The story conveys the shape of Kel's days without dragging, never letting go of the need to stop the source of the killing machines as soon as she can.