Is it too much of a coincidence that Mr. Carmichael comes back from Moscow the very day that Sara needs to return the monkey to Mr. Carrisford? Perhaps, perhaps. Chapter 17 opens in expectation of this event, with three of the Carmichael children paying a friendly visit to the Indian Gentleman to cheer him up, such that they will also be conveniently at hand when their father (and later Sara) arrives. The scene has the feel of a carefully orchestrated stage setting, and so perhaps it is.
We are told a brief summary of why the trip has been so drawn out...which it must have been, for as we recall, it was the very night that he left on the journey that Sara's attic was first magically transformed. So Carmichael's trip needs to have been long enough for Sara and Becky to become accustomed to their good fortune, and to show the effects of being well-fed and happy. We also get a lovely little character sketch of Donald Carmichael (the boy who gave Sara his Christmas sixpence) as a boisterous and imaginative child, and a more mixed sketch of Janet Carmichael as too-soon becoming a little responsible mother figure. It's Janet's task to do emotional work for Mr. Carrisford, reassuring him that it wasn't his fault about losing Captain Crewe's money. (I have some odd flights of fancy about Janet's later life, but this isn't the place for them.)
In the midst of the conversation about the hunt for Captain Crewe's lost daughter, the storylines begin to cross. The Carmichael children explain that they call the lost girl "the little un-fairy princess", imagining what her life will be like when she discovers that she's a fabulous heiress. For them, she is a princess not because of behaving like one (Sara's basis for her princess identity) but because of these external trappings. And out of nowhere, Donald brings up the "little-girl-who-is-not-a-beggar" (i.e., the real Sara, whom they've been observing) and how she has nice new clothes and maybe she has been found by someone after being lost, just like the un-fairy princess will be. And of course, she has, it's only that none of them quite know it yet.
Carmichael, after traveling all the way back from Moscow, fulfills dramatic story requirements by coming directly to Carrisford's house to make his report (rather than going home to freshen up first), though perhaps this is only kind of him to avoid drawing out the suspense. The fact that there is no little girl accompanying him tells its own story. The Carmichael children are shooed away and Carmichael reports that the girl in Moscow--though having superficial similarities--is not Captain Crewe's daughter and they must begin the search anew.
And here's where I'm willing to forgive certain coincidences that only shorten, rather than entirely enabling, the resolution. For Carmichael suggests that rather than searching schools in Paris, on the assumption that Sara was sent there due to her mother's origins, they should try schools in London, because her father was British after all. And Carrisford immediately thinks of the school next door, casually mentioning the poor child there that he's taken an interest in, but simultaneoulsy rejecting the notion that the "dark, forlorn creature" could possibly be the daughter of his bright, golden, happy friend Crewe. Of course, the moment Carmichael would approach Miss Minchin and ask after the possibility that she knew anything of an orphan girl named Crewe, the mystery would be solved. So I'm happy enough that it's at this very moment that Sara knocks on the door to return the monkey, and that Ram Dass comes in to suggest that Carrisford might want to meet her in person to thank her--knowing, of course, that she's the object of their magical charity (and knowing that she doesn't know it).
It doesn't take any special literary analysis skills to know that All WIll Be Revealed in the following scene. But the revelation is multi-layered and delicious, so I'll save it for it's own entry.
Oh, but one more thing. Since this series is my expiation for loving ALP despite its problematic aspects, I must note that we're treated to one more bucket of icy-cold Orientalism when Carrisford notes that having planned The Magic together, it was only possible with "the help of an agile, soft-footed Oriental like Ram Dass" because it's necessary to evoke the sterotype of a "magical" Indian servant who can move without being heard and act without being seen. The wording turns this from Carrisford acknowledging the assistance of someone more mobile than he is (in his convalescence) to turning Ram Dass into something of a supernatural figure.