High Time for Heroes (Magic Treehouse #51, Merlin Mission) Hardcover by Mary Pope Osbourne

Jack and Annie are on a mission for Merlin the magician!

This time, the magic tree house whisks them off to Thebes, Egypt, to find Florence Nightingale, a world-famous nurse. But when they find her, the Florence Nightingale they meet is not a famous nurse at all--she's not even a regular nurse! Have they found the right person? Or did Merlin make a mistake? An easy mission turns dangerous when Jack and Annie try to solve the mystery before it's too late.