A UFO crash-lands in the Central Park Zoo. Colonel Robert Hayward of Air Force Intelligence and his team enter the craft and, after killing a hostile ape-like creature, find a slightly more humanoid prisoner, who at first speaks Russian and then English.
The alien, named Hes'bu, reveals that his people, the Oinn, have been listening to broadcasts from Earth and learned the two most commonly-heard languages (the Cold War being still on and all). The Oinn are at war with the Blettr (like the hairy creature that attacked the soldiers), whose fleet is preparing to enter the Solar System and attack Earth. The Oinn offer their help, but they need to set up a base in the Antarctic with weapons capable of fighting off the Blettr. In return, they need tons of radioactive material to power the weapons. Both of Earth's superpowers agree to the Oinn terms, with Rob Haywood being chosen as the American liaison with the aliens, and a linguist named Nadia Adrianova as his Soviet counterpart.
The Battle of Earth begins...
The following tropes are present in the novel:
- Aliens Speaking English: Justified, as the Oinn and Blettr learned English and Russian by listening in on broadcasts from the US and USSR. However, Nadia starts learning the Oinn language. She starts to get suspicious when she realizes that the Blettr are using the same exact language. During the meeting with the Blettr leaders, Rob and Nadia switch to Spanish in order to talk privately, as the aliens didn't bother to learn it.
- Aliens Steal Cable: Both alien races have learned English and Russian by listening to our broadcasts.
- Apes in Space: The Blettr have hair all over their bodies and look more beast-like than the Oinn.
- Apocalypse How: Two large cities get destroyed by Orbital Bombardment during the battles with the Blettr: Denver and Tomsk. Each city has roughly half a million people in it. Naturally, both the Americans and the Soviets are very eager to get to the bottom of this.
- Bittersweet Ending: The aliens may be defeated and sent packing, but at least a million people are dead, and, according to Nadia, humans may have lost their one chance to extend a hand of friendship to an alien civilization.
- Black Box: The ground-based weapons built by the Oinn in their Antarctic base. They seem to work, but they don't allow humans to look inside them. That's because there's nothing inside. They're not weapons, they're just there to fool humans into supplying the Oinn with radioactive material. The "battles" are just simulations for the humans' benefit.
- Brandishment Bluff: Near the end, when all the gloves are off and the aliens are threatening to drop bombs on human cities if their demands are not met, the military informs them of a secret laser weapon that can obliterate any ship in orbit. The aliens call the bluff, Rob picks up the phone and says "Fire!", and the alien ship explodes. The rest of the aliens are hesitant, even though no weapon fire was detected (then again, a laser would be kinda hard to detect). It turns out that the soldiers simply planted charges on the ship, when it was on the ground, and detonated them on command. The next bluff is against The Mothership on the other side of the Moon. The American general claims that NASA has secretly planted nuclear mines all across the Lunar surface. Unwilling to test that hypothesis, given what happened to the other ship, the aliens hightail it out of the system. When Nadia asks the general if that's true, he smiles and tells her it's classified.
- Chummy Commies: The Cold War is forgotten for the duration of the invasion, and both superpowers work together. The Final Battle even has a joint force of American and Soviet troops assaulting the Antarctic.
- Came from the Sky: The novel starts with an object falling from the sky, except it doesn't follow a straight trajectory and changes course once or twice, before crashing in Central Park Zoo. The object crushes a man, and also kills a young woman and her child (Death of a Child happens right away).
- Crazy-Prepared: When Rob first shows up in Central Park, he tells the NYPD captain that they'll be following a specific plan. The surprised captain asks if the government has anticipated a UFO landing. Rob explains that no, not exactly, but the plan covers a wide range of extreme situations.
- Cunning Linguist: Nadia is an expert at languages. She, at the very least, speaks fluent English and Spanish. She's also studying the Oinn language and is shocked to discover that the Blettr speak the same language. Rob also knows some Spanish, although that's not that unusual in the US.
- Death Ray: The Oinn claim that the installations at the Antarctic base are radiation-based weapons. It's a lie, they're just empty shells. During the climax, when the aliens drop all pretense and threaten to drop bombs on cities, if their demands aren't met, the humans claim that they've secretly developed a powerful anti-space laser weapon. When the aliens laugh at the idea, Rob picks up the phone and says "Fire." The alien ship blows up. It was a bluff, Rob's team has simply placed a bomb on the ship, which was triggered when by his subordinates, when he said "Fire."
- The Empire: The Oinn portray the Blettr as an aggressive interstellar empire, who seeks to subjugate or destroy all other races. In truth, both races are The Remnant of their once-great civilizations, traveling in beat-up ships and turning to planet looting to sustain them. They have no idea where their homeworlds are or whether they still even exist. There is no longer any enmity between the Oinn and the Blettr, they just use this as part of their con.
- Fast Tunnelling: The Blettr have a giant worm-like machine that can quickly move through the lunar rock.
- Final Battle: The joint American-Soviet assault on the Oinn base in the Antarctic, mainly composed of soldiers from the destroyed Denver and Tomsk and led by Rob. The battle is bloody on both sides, but humans are successful in the end. Most of the Oinn at the base are either killed or captured. The captives are placed in one of their ships and sent into orbit, while the other ship is kept by humans for study.
- First Contact: Rob makes contact with an Oinn named Hes'bu, who appears to be held captive on a ship belonging to another race called the Blettr, one member of which he and his team have killed upon entering the UFO, and two others were found killed during the crash. It turns out the three Blettr on the ship were already dead and were placed there to sell the story. The one, who attacked the humans, was being controlled by a special device, despite being dead. Later, Rob and Nadia travel to the Moon in order to make an official contact with the Blettr, who tell them that they're the good guys and the Oinn are the villains.
- First Contact Team: After the spacecraft crashes in the middle of New York, an army general steps out of a helicopter and announces that he's taking charge of the situation...and is arrested by the police captain who's actually in charge. The next military man to show up is the protagonist, an Air Force Intelligence officer who respectfully offers the captain some intelligence and practical advise (which is taken), then waits quietly while a team of scientists and military brass dispatched by the President argue. When it's time to enter the craft, he takes a Sergeant Rock with a .45 as protection, and an electronics specialist with a cable-fed camera (the cable guarded by its own team of soldiers).
- Human Aliens: Averted. While both races are can be called "humanoid", it's only in general terms. The Blettr look like Apes in Space, and don't actually have a single huge neural cluster (i.e. the brain). The neurons are spread all over their bodies, making them harder to kill. The Oinn look slightly more humanoid, but they don't have any necks, body hair, or wrinkles. Their eyes are compound (like insects), and their mouths are just slits near the bottom of their heads. They have asymmetrical flaps on the sides of their heads that may be used for breathing.
- Imported Alien Phlebotinum: Averted, the Oinn keep brushing off the human attempts at getting a closer look at their technology due to the war, and the all the systems on the Blettr ship that crash-lands in Central Park burn out. Neither race has any intention of giving humans their technology. Hes'bu deliberately burn out the systems on the crashed ship in order to keep the technology out of human hands. They are Planet Looters, who are trying to convince humans to supply them with radioactive material for their reactors and weapons. At the end, though, the humans force both races to leave a small ship behind for humans to study.
- It Only Works Once: A version of a bluff that only works once. When the crew of an alien ship threatens to drop radiation bombs on Earth cities, the military replies that they have a secretly-developed laser weapon trained on the ship. The aliens try to call their bluff, but their ship promptly explodes. Turns out there is no laser weapon after all, but the soldiers simply planted charges on it earlier. The remaining alien ship, after a few more words, wisely decides to leave and not challenge the bluff.
- Love Interest: Averted, Rob and Nadia become friends, but they're too different (a soldier and a linguist) to ever become lovers, and the events of the novel are hardly conducive to romance. Besides, the ending of the novel may have put a permanent end to their friendship (besides, they're on opposite sides of the Iron Curtain).
- The Mothership: A Blettr fortress ship manages to get through the Oinn defenses and lands on the other side of the Moon, where the Oinn defenses can't touch them, while also giving themselves a prime location for launching assaults on Earth.
- Ray Gun: Both races have blasters that can cut a human in half with a single shot. Since the Oinn claim that all their weapons are radiation-based, it's implied that this applies to their handheld weapons as well.
- Reverse Relationship Reveal: An alien spacecraft crash-lands on Earth, after being hijacked by a different alien race. It is subsequently discovered that the peaceful alien race is being set up to look like aggressors by the aliens who actually want to take over Earth. Well, actually, both races are in cahoots and are really just scamming humanity.
- Scientist vs. Soldier: There is some conflict in the novel between Colonel Rob Hayward and the linguist Nadia Adrianova. The former, naturally, sees everything from a military viewpoint, while Nadia is a civilian. At the end, Nadia admonishes the military for destroying an alien ship and bluffing The Mothership into leaving the system, when humanity could've extended a hand of friendship to the aliens. On the other hand, the alien ship she was talking about has just threatened to drop radiation bombs on cities, and the aliens have already wiped out two cities, killing over a million people, and the fortress could have done the same. Fact is, the military may have been right here, given the aliens' intentions.
- Self-Destruct Mechanism: When the humans first find Hes'bu aboard the UFO, he claims that the Blettr have set the self-destruct on the ship in order to take New York with them, after realizing they were going to crash. He manages to avert it. It was a lie, there was never any self-destruct. The ploy was just a way for Hes'bu to burn out all the systems aboard the ship to keep the humans from studying the technology.
- Space Nomads: Both races turn out to be this, after a Great Offscreen War that has destroyed their civilizations. Formerly enemies, their descendants have formed a new culture that sustains itself in what's left of the fleet by finding a primitive race and convincing them to supply them with resources, pretending that the Oinn and the Blettr are still enemies. For the humans, the Blettr were chosen as the aggressors, as they look a little more alien to us than the Oinn (not by much, though).
- Take a Third Option: The Oinn build a base in the Antarctic that protects Earth from the Blettr, depanding a steady supply of radioactive material to power it. The Blettr claim that the Oinn are the bad guys, and they want the humans to supply them with radioactive material to help with the war effort. So what do the human higher-ups decide? Attack the Antarctic base to see what's really going on, something the Blettr told them not to do. It turns out both races are working together to syphon as much radioactive material from Earth as possible.
- Tyrant Takes the Helm: A general arrives via helicopter to the site of the crash-landing and tries to take charge. The NYPD captain is having none of that and has him arrested for trespassing. The helicopter pilot is smart enough to immediately take off.