Mysterious objects falling from space into the ocean are the beginning of a series of strange events that are eventually discovered to be the work of aliens from another world, apparently one with a much thicker atmosphere so that they feel more at home in the ocean depths and may not even be able to survive up in the air. Attempts to contact them go badly, and it turns into a war for control of the planet.
This novel contains examples of:
- Brand X: The main character works for the EBC (English Broadcasting Company). It gets extensively lampshaded — a Running Gag is that every character is introduced saying "don't you mean BBC?", and later gets subverted, when the government takes over the media and the narrator explicitly mentions that the EBC and BBC are now one and the same.
- Covers Always Lie: An at-least-they-tried example from a Penguin edition that shows an ocean liner being sunk/attacked by an alien bio-tank. Ships do sink in the novel, and there are alien bio-tanks, but they never appear in the same scene.
- Expy Coexistence: The main character works for the EBC (English Broadcasting Company). A Running Gag is that every character is introduced saying "don't you mean BBC?".
- Hidden Supplies: The narrator Mike learns that his wife's "hobby" of bricklaying was cover for her bricking up a cellar-full of food supplies in case of disaster. "Did you really think that someone like me would be doing all that bricklaying just for fun?"
- Hostile Terraforming: Humanity sees indirect evidence that the invaders are reshaping portions of the ocean floor. They also melt the polar icecaps, but that is more likely an attempt to disrupt human civilization rather than terraforming.
- Inscrutable Aliens: A group of aliens invades the Earth's oceans. They never contact the human race in any way and the two sides engage in a war without either side ever seeing the other face-to-face.
- Market-Based Title: The first American edition was titled Out of the Deeps.
- Military Mashup Machine: The aliens drive their amphibious tanks from the deepest parts of the ocean up to the coast to attack humans.
- Organic Technology: The only major example of the aliens' technology in the story is their hideous "biotanks," which are armed with immobilization weaponry and apparently abduct humans down into the deep for some horrible fate. Their surface is also heavily armored, immune to small-arms fire, but flexible and able to squeeze and expand like balloons.
- Poor Communication Kills: This compounds throughout the early parts of first contact, with tragic results. Human anti-air defenses shoot down a lot of alien craft before they fully appreciate they are alien craft, and then when they send down bathyspheres to try to examine what they're doing down there, the bathyspheres use ultrasonic sensory equipment that apparently causes them great pain, causing the aliens to lash out, killing the crew. Humans respond by atom-bombing their settlements, and it's all downhill from there.
- "Ray of Hope" Ending: At the end of the story the invading underwater aliens have melted the polar ice caps and caused worldwide flooding. However, the Japanese have developed an unmanned device that broadcasts ultrasonic waves lethal to the aliens. It has wiped out some of the aliens and might succeed in destroying all of them.
- Red Scare: Mocked with the minor character of Tuny; she continues to insist the Russians are behind the book's ever-escalating attacks on humanity from the depths of the sea, when it's soon made clear they couldn't possibly be doing it.
- So Was X: Two reporters are discussing a brilliant but somewhat eccentric oceanographer who is claiming that the mysterious fireballs falling from the sky over the deepest parts of the ocean, the discolouration of certain currents from a spike in sediment levels and the disappearance of several bathyscapes is a result of alien invasion. One of them points out that however crazy the idea sounds, the man does have an explanation for more of these inexplicable events, that are equally inexplicably happening simultaneously, than anyone else. His colleague has the following response: "So, undoubtedly, would Jules Verne."
- Tentacled Terror: The story is about the invasion of Earth's oceans by a race of alien cephalopods. (Or at least the organic weapons they deploy are somewhat squid-like; it's never revealed what the actual aliens look like.)