(Frontispiece from Wet Magic, 1913.)
(Illustration from the 1913 edition of Wet Magic.)
Wet Magic isn't my absolute favorite of E. Nesbit's fantasy novels (that's The Enchanted Castle), but it is charming and entertaining, and if you like mermaids you shouldn't miss it. It's about some children who rescue a mermaid from a sideshow at a fair, and then travel to an underwater realm of merpeople, sea urchins, and narwhals.
(Wet Magic is also recommended reading for those who like narwhals.)
This book is also, basically, about books. The children summon the mermaid by quoting poetry by Milton ("Sabrina" from Comus), and they're constantly talking about books, both the good ones that they love and the bad ones that they are forced to read by their unsympathetic aunt. The good books are mainly historical romances, poetry, and fantasy stories. The bad ones -- as we all could have guessed, right? -- are moral tales for children. In the end, the books come to life, and there is a literal war between good and bad children's literature.
(Illustration by Arthur Rackham of Milton's Sabrina and her nymphs.)
Wet Magic isn't free for your Kindle -- it's 99 cents. But for 99 cents, you get grouchy mermaids, ferocious narwhals, a plucky carnival boy, and a tour through a lovely, pearly underwater kingdom. So this book is going on my virtual bookshelf.
(Puck Magazine, September 1913; image from here.)