One of my favourite episodes in the whole series is here, when the expedition tries dowsing for water and the only one who succeeds in getting any response from the hazel twig is Titty (though Dorothea, of course, desperately hopes it will be her...) I think this is the only vaguely paranormal event in the Swallows and Amazons universe, but there is no doubt at all that Titty experiences what she does, and that the water is really there. I love her initial fright and resistance, and her courage in overcoming her fears, which to me makes the discovery of the spring more exciting than Roger's finding of the gold (though that is fun, too).
Titty really comes of age in this book -- she's the one who leads the others through the hill after the tunnel collapses ("Pudding Heads"), and she leads the other able-seamen in fighting the fire. I'm glad to see the developing friendship between her and Dot (I love when Dot reads her novel aloud!), and the whole mix up with Timothy the armadillo, and the lovely quiet scene at the very end when the hedgehog returns to the well. A very enjoyable installment!