The title of this fantasy, Impossible Creatures, might just as well refer to Katherine Rundell herself , whose career seems almost too extraordinary to be true. At the age of 36, she has written eight books and an award-winning play; she has been appointed the youngest female fellow at All Souls College, Oxford; and she was the youngest person to win the Baillie Gifford Prize for non-fiction, awarded for Super-Infinite, her 2022 biography of John Donne.  Her five children’s novels, including Rooftoppers and The Explorer, have all appeared to ecstatic reviews, typified by this comment (quoted on the cover of her newest book) from Michael Morpurgo: “There was Tolkien, there is Pullman, and now there is Rundell.” On her website, Rundell says that in her spare time she’s learning to fly a small aeroplane; if she looks down, she might consider that she has a long way to fall.  But put away the parachutes: her latest book – the first in a trilogy – is another triumph.…