Disturbing events in the world's oceans alarm scientists around the globe, launching an investigation into a mysterious threat to humanity's fragile existence.

While Venice suffers an unprecedented plague of jellyfish, it's discovered that a mutated bacterium is the cause of a growing number of deaths on the coasts.

Political leaders grow skeptical about the dramatic situation on the French Atlantic coast, while the ice worms on the sea bed continue to spread.

Dr. Cécile Roche detects in crabs that have overrun coasts around the world the same bacterium that entered drinking water on the French coast via infected lobsters.

Johanson suspects that an unknown marine intelligence, which he calls Yrr, is behind the strange happenings, and wants to contact the life form.

The expedition to study the Yrr sets out for the Arctic, where a large number of Yrr signals were spotted.

With humanity's future at stake, the team butts heads on what to do. In a desperate situation, a radical decision is made.