Sigur Johanson is a wormologist (He's actually a biologist at the university Trontheim and an expert for worms). Accidentally, there's a strange species of deep sea worms that eat a lot of stuff with complicated names. Things threaten to collapse on a continental level. Basically, the world as we know it will crumble under the impact of worms (so far so awesome).
Leon Anawak is a whalist (he's a maritime scientist and studies whale behaviour) and is taken aback when he watches whales attack boats and kill people. *gasp*
More bad things happen: jellyfish kill people, ships collide, there's a suspicious absence of the Gulf Stream, a massive crab attack, an epidemic in France (because of exploding lobsters) and - I almost forgot - a tsunami that kills a few million people and destroys most cities close to the Baltic Sea (the worms!!! Where's Kevin Bacon when you need him?).
Tina Lund dies (This is the first in a serious of unrelated characters doing unrelated things with no impact on the main plot (I lied. It's not the first, but at one point I stopped counting).
Naturally, all events are related. After what feels like 500 pages, the world is in shambles.
Even though most of the damage has been done in Europe and the main protagonist is from Europe, the Americans start a task force (they kidnap every scientist and order them to... be scientists).
They all go to a castle in the mountains for research. After all the above mentioned coordinated attacks that have picked up speed, culminating in the Tsunami and forcing the world to react as a unity, what do you think happens? Exactly! Nothing. For excruciating months and about 800 pages, nothing really happens. This is because- Oh, look! An unrelated character is doing something unrelated! Shiny!
The attacks stop and there's research going on. Kind of. Actually, everyone does a little bit of puttering around.
Johanson, who's not only a wormologist but a strange-thingologist, develops the following theory (we instantly know that he's right): There's an unknown species living in the depths of the ocean since the beginning of time. They are doing things because- Oh, look! An unrelated character is doing something unrelated! Shiny!
The Yrr (just for the record, I think that's a stupid name) are single-cell organisms and operate like tiny Borg (--> The Star Trek works because the book swings the moral bat worse than Captain Picard, sadly without having any of his boyish charm).
Then there's a 400 page description of someone's father's funeral.
Then everyone goes on a ship.
Let's just think about this for a moment. There's something in the ocean that makes every creature in it go wonky, and that has the power to stop the gulf stream. Is it reasonable to put every scientist who has even the slightest chance to fight back on the same ship and let them sail off into the deep sea? Obviously it is, because the book expects you to believe this is a good idea.
There's a secret lab that we know must be there when we read the word 'ship' for the first time, but we need about 300 pages to discover it. Then we need another 600 pages to get inside the lab, and really, it's unexciting.
I feel I should mention the evil American antagonist with Asian background, General Li (American Navi General, think about it for a moment). General Li (navy) is such an outrageously clichéd villain, though, that I refuse to admit her existence.
The person representing the United States (the one I don't want to discuss), wants to kill all Yrr, and she knows how to do it. Somehow we're made to believe that killing a species who's determined to erase mankind and destroys half of the earth while doing so is a bad idea.
Instead wormo-thingologist Johanson, develops a communication method that involves a dead man, Yrr-pheromones, mini submarines and blowing himself up in the middle of a tremendously boring 800 pages showdown. Don't ask - only MacGyver can make that explanation sound reasonable.
BTW, if you ever asked yourself how you can possibly make trained military dolphins boring, read the book! It's a great step by step guide.
Then we finally realise, why during the last 2,000 pages, we've constantly read about Karen Weaver. You don't need to know anything about Karen Weaver except that she was somehow around, is the token female character and love interest of... uh... someone. She is now saving the world after Johanson's (and navy general's) death. Obviously she does that by kidnapping the already mentioned dead body with a mini submarine. While she remains in the boat, the body bravely jumps into the water to communicate with the Yrr. HUSSAH!
The attacks of the Yrr stop then, because the dead body which is full of their natural pheromones and... Alright, I give up.
The book ends.