Plunged way back into the past, Rain, Emily, and the rest of the Dinosaur Explorers, continue to make their way back to the present, but first they must take the plunge and submerge themselves into the prehistoric oceans. What they find is that the weightlessness of the water caters to larger creatures, sometimes bigger than dinosaurs themselves! Here they must dodge carnivorous ancient dolphins, elude massive crocodile creatures, and essentially do their best to survive. But it's also possible that they may even find some undersea friends. One thing is for certain, the Dinosaur Explorers are in way over their heads! Will they sink or swim?