Osborne, Mary Pope <br/><br/>
Dark Day in the Deep Sea:  Magic Tree House #39. 

 - New York, NY :  Random House/ A Stepping Stone Book,  2008. 
 - Magic Tree House .
<br/><br/> When eight year old Jack and his seven year old sister, Annie, join a group of nineteenth century explorers aboard the HMS Challenger, they learn about the ocean, solve the mystery of it's fabled sea monster, and gain compassion for their fellow creatures. 
<br/><br/><label>ISBN: </label>9780375837326