SCHOOL IS OUT AND SUMMER HAS ARRIVED. AFTER FOILING Dr. Catalyst, Emmet was hoping he and his father might be able to return to Montana. But working to undue the damage already caused by Dr. Catalyst is a big job. And now Dr. Doyle has been permanently assigned to Everglades National Park. Instead of heading west as he hoped, Emmet grouses about spending a summer in the hot, humid Florida sun.

But it isn’t just a longing for the mountains that pulls at Emmet. He can’t rid himself of the feeling that Dr. Catalyst is out there somewhere. Everyone else believes that he died in the swamp or that he’s finished and hiding away somewhere licking his wounds. But Emmet doesn’t think someone so committed to his cause would give up so easily. And the occasional nightmares of the fearsome Pterogators Dr. Catalyst created aren’t helping him any.

To celebrate the start of summer, Dr. Geaux and Dr. Doyle take Emmet, Calvin, and their friends to a nearby cove for snorkeling. The water is warm and crystal clear, but the reef below them is swarming with Lionfish … and devoid of other sea life. Emmet learns that much like the pythons and boa constrictors of the Everglades, the Lionfish are another invasive species that are devastating the marine ecosystem.

Then, without warning, a group of odd fish appear from the depths of the cove. They look like a cross between the great barracuda and the moray eel, and they begin quickly devouring the lionfish right before the kids’ eyes. These strange creatures are big, fast, and have mouths full of razor-sharp teeth. Emmet starts to get an eerie feeling. The speed and strength of the fish are almost unnatural.

The creatures also have voracious appetites. After clearing the reef of Lionfish in a matter of minutes, they soon turn their attention to Emmet and his friends. All Emmet’s worries about Dr. Catalyst suddenly take a backseat as the strange fish begin heading straight for them. Right now he’s only got one thing on his mind.

Survival.