Dark Day in the Deep Sea

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Dark Day in the Deep Sea is the 39th book in the Magic Tree House series by Mary Pope Osborne and illustrated by Salvatore Murdocca. This book takes place in the 1870s during the time of the first major oceanography expeditions. Jack and Annie have to find the third of four secrets of happiness to share with Merlin the Magician so he can find joy in his life again.

Here is the plot: Jack and Annie wind up stranded on an island, until a ship of explorers and scientists comes along and rescues them. But there's more than this in store for the series regulars. They dip into the sea and find themselves stranded and hopeless again---but in the gigantic arms of a sea monster!

This book, as well as its Magic Tree House Research Guide Companion, 'Sea Monsters', were released in the US on March 25, 2008.