People all over the world experience bizarre encounters involving strange new creatures in the oceans. Among those people are Laura Daughtery, a marine biologist and single mother working in California, Richard Connelly, a Louisiana family man fishing in the Gulf of Mexico, and Miles Bennett, a North Carolina teen who finds one of the creatures' eggs.

After a mysterious animal carcass is discovered on the shore of Sullivan's Island, Laura and Rich head there to look for some answers but instead get detained for questioning. Also, a team of scientists face a hazardous autopsy of the deceased creature. Meanwhile, Miles decides to name his new discovery Nimrod but faces panic and trouble when Savannah throws a party at which point Nimrod ends up escaping.

The phenomena becomes more widespread as similar creatures wreak havoc on the coast of Texas. Laura gets more upset after she loses her job, while Rich still has a difficult time getting over the loss of his brother. Rich's situation gets worse when he starts to hear his brother's voice when he is near water. Cirko and Lee find that the creatures have been digging under the ocean bed, which could link them to global warming. Meanwhile, Miles discovers that it's not safe to raise Nimrod in the backyard when lightning strikes.

Laura and Richard reunite and use a GPS device to track one of the creatures to a local pier in California while Cirko and Lee consider asking Laura to join them in their investigation. Meanwhile, Miles and Phil fight to keep Nimrod a secret when suspicious Animal Control officers search for a missing neighborhood dog.

Cirko's life is in danger after he discovers the origin of the mysterious new species. Laura and Rich begin to fear for their own safety when they come into possession of a much sought after sea orchid. Miles sneaks Nimrod out of the house when his parents realize that he's been secretly keeping the animal as a pet.

Jackson comes to Laura and Rich's aid after they find that Laura's home has been broken into. Miles gets in trouble with the law in his attempt to free Nimrod. And Lee discusses Cirko and the creatures with his superiors.

Jackson helps Laura and Rich build a submersible so that they can visit a site where the creatures spawn. Meanwhile, the Bennett's consider boot camp as a way to discipline Miles.

Trapped in the submersible, Laura fears survival is impossible while Rich begins to hallucinate. Miles worries about Nimrod when he hears of trouble at the marine docks. Phil helps Miles look for Nimrod but they discover something else.

Laura and Rich are in for another shock when they leave the ocean floor and return to the surface. Meanwhile, Savannah suspects that Nimrod's responsible for Miles ending up in the hospital.

Laura and Rich decide that it's time to get some answers from Lee as Laura considers going back home. Meanwhile, Miles gets in trouble with the local residents after a violent incident with a bully.

As a massive tsunami heads for the east coast, Laura must save Rich by heading to North Carolina where Miles and his family are trying to escape with their lives.