"Little Pedro is now a member of the Adventuremice, a group of daring rescuers--so when he discovers a strange, lost little mouse in the ocean, and realizes he's found a mermouse, he knows he has to find a way to take the mermouse home. As the Adventuremice explore deep beneath the water to return the mermouse to its family, they may just discover a grand, secret city and surprising new friends..."--