Eve of the Emperor Penguin — Mary Pope Osborne

For the final secret, you must go
To a burning mountain of ice and snow
On wheels, by air, then all fall down,
Till you come to the Cave of the ancient Crown.

So says the rhyme Jack and Annie get to guide them on their mission to find the fourth secret of happiness for Merlin the magician. This time, the magic tree house whisks them to the super-cold continent of Antarctica -- the land of ice and snow and penguins. There they meet a group of scientists and reporters, and are surprised to discover that they are in contemporary times! How will they find a burning mountain or an ancient crown if they're with these people? Even a disaster or two can't stop Jack and Annie from finding a way!

Mary Pope Osborne deftly combines science, magic, and the joy of nature in this thrilling adventure for young readers.