In the second book of the series, our young adventurers must travel to the dangerous Dark Depths of the sea in order to help their good friend, Zarden the Sea Dragon, whose father has become very ill. Along the way, they will face the dreaded Megatooth, a savage, deep-sea prehistoric shark. They will also encounter someone from Zarden's past, but are they friend or foe? While all of this is happening, they will discover that Safe Haven, the home of the sea dragons, has a "mysterious" secret. Most importantly, will they be able to find the medicine needed in time to save Zarden's father?