As the third book in Lucy Boston's "Green Knowe" series, readers who are moving through the books chronologically may be a bit surprised at the extreme change of formula in the story that dictated the two previous books. There is no Tolly or Grandmother Oldknow and their discoveries of past inhabitants of the house, but rather two elderly women who rent the house and send away for a niece and two children from "the Society for the Promotion of Summer Holidays for Displaced Children."
Thus "The River at Green Knowe" is definitely moving in a different direction from the previous books, and continues with Boston's decision to set most of the scenes upon the river, as Ida, Oskar and Ping explore the flooded areas and the islands around the ancient house, often meeting strangers who are just as Displaced as they are. The adventures that they experience are dreamy and mysterious within the shrouded waters and woodlands, and one is never quite sure whether they are dreams or reality save that all three of them experience them.
These exertions are also different from Tolly's adventures in that they are more magical experiences rather than ghostly, and therefore need readers to suspend disbelief a little further. The fact that the children's experiences are all quite separated from each other and episodic also makes them a tad uneven. Some are based more on naturalistic themes, such as an overgrown river-side house, witnessing a pagan-festival in a time-travelling moment and meeting a busman who wandered into the woods and decided to remain there always, whilst others are of the extraordinary type: an island of winged horses, a giant who doesn't know what laughter is but eventually joins the circus, and one of the children shrinking down to mouse-size. Needless to say, Boston's style is suited best to the more natural occurences that just border on the supernatural. To me at least, the others come across as a little *too* odd.
However, there is a theme that hasn't been addressed before that pushes through: that of adult disbelief in Green Knowe's magic. Beforehand, all strange events were simply taken in their stride by Tolly and Grandmother Oldknow, whilst here Boston explores the idea of grown-ups not being able to see what the children can. Green Knowe is contrasted against the reality of adult ignorance, whether it be through a frightened, confused message in a bottle, or through Boston's first two comic figures Maud Biggin and Sybilla Bun, who cannot see the truth in front of them even when they've been searching for it.
It all goes hand in hand with Oskar's comments on thoughts being real, and Terak telling the children he is so big that no one sees him. Boston weaves these ideas through her narrative with ease, and as always her poetic language is utterly beautiful. I don't think Oskar or Ida were quite as well defined as Tolly or as Ping becomes in later books, which is a shame as they had the potential to be fascinating - and they don't appear in any later books. However, keep a look out for a dark figure examining the the house that *does*.