The plot concerns the crew of a spacecraft led by Commander Hal Morton landing on a barren world where they intend to perform an archaeological survey. The group encounters a strange, black-furred, feline alien known as Coeurl, who is apparently the only living thing left on the planet. The creature makes chemist Gregory Kent uneasy, and he advocates eliminating it just in case it's hostile. However, as Coeurl makes no threatening moves of any kind, Commander Morton sides with the expedition's biologists who want to take "pussy" in for study.
Coeurl tamely comes aboard the group's ship, and allows himself to be studied by the humans. In fact, they grow so used to his comings and goings that, aside from Kent, they start taking "pussy" for granted. That is until crew member Jarvey, a friend of Kent's, turns up dead of unknown causes after wandering away into the ancient ruins.
Kent suspects Coeurl — as there is no other life on the planet that they're aware of. It turns out, of course, that he's right; Coeurl is actually the last remaining member of a species that eats the id of living things and had previously wiped out all life on this world. And now he is plotting to steal the humans' ship and escape... after he's done killing them all one by one and absorbing their id, of course!
The story was incorporated into the novel The Voyage of the Space Beagle, and both there and in its original form has been massively influential over the years. Coeurl-like creatures have turned up in everything from Dungeons & Dragons to Final Fantasy. The plot of Alien was similar enough that van Vogt took screenwriter Dan O'Bannon to court over the matter.
This story provides examples of:
- A Dog Named "Dog": Coeurl. He's a Coeurl named Coeurl (never reffered to as "a Coeurl" or even "the Coeurl").
- Cats Are Mean: Okay, so the creature isn't really a cat, but he's cat-like and he's definitely mean.
- Combat Tentacles: Coeurls have two tentacles growing from their backs. The one in the story uses them to grab his victims and break their necks.
- Commanding Coolness: Hal Morton is The Captain and your typical manly man's "two-fisted scientist" hero in these kinds of stories, and he holds the rank of Commander.
- Death World: The unnamed planet the crew comes to explore and where Coeurl lives. Although archaeologist Korita attempts to explain the demise of civilization through The Cycle of Empires, it's really because everyone was killed by the Coeurls over the centuries. The planet itself is desolate and deserted, with only a single member of the race responsible for killing all the other life still living on it, completely by himself.
- Go Mad from the Isolation: Prior to the arrival of Morton's expedition, Coeurl has reached the point where because he is alone and has no one and nothing to interact with, he is little more than an animal, driven purely by hunger and instinct. Encountering the human explorers and seeing their technology brings him back from the brink, making him remember how to think and reason... unfortunately for them.
- In-Series Nickname: "Pussy" for Coeurl.
- It Can Think: Coeurl may seem like an animal, and the crew treats him like one at first, but he is actually incredibly intelligent and cunning. He doesn't start the story this way, though; when he's first introduced, isolation and the daily battle just to survive has regressed him to an animalistic state, but encountering other intelligent beings makes him remember he too is an intelligent creature, and his reasoning returns to him, allowing him to begin scheming against Morton's crew.
- Japanese Politeness: The expedition's Japanese archaeologist Korita is portrayed this way.
- Last of His Kind: Coeurl. There are no other Coeurls in existence after so long, at least on that world.
- Locked Room Mystery: Coeurl's M.O. once he's aboard the ship is to secretly leave his cage, kill a crew member and eat their id, then return to the cage before anyone notices he's gone, so as far as everyone else is concerned, it's a complete mystery how the murdered crewmen died.
- Panthera Awesome: Coeurl is a big black alien feline.
- Picky People Eater: The monster only wants to eat your id.
- Pragmatic Villainy: Except for Jarvey, the alien avoids killing any of the humans outside the spaceship if he can help it, as he wants to gain the crew's trust. He only killed Jarvey and ate his id because he was essentially mad with starvation. Once his hunger has been sated, he waits until he's actually gained entry to the ship before he starts killing people again, and even then, he commits the murders in a manner explicitly designed to divert suspicion from himself.
- Properly Paranoid: Kent's first instinct upon encountering the alien is to shoot it, and even when everyone else pretty much adopts the thing as the expedition's mascot, he keeps trying to convince everyone that it's dangerous, and even goes as far as attempting to feed it poisoned food. It turns out he was right.
- Ten Little Murder Victims: A good chunk of the plot concerns Coeurl stalking and killing the ship's crew.
- Trapped with Monster Plot: The expedition members don't know it, but their feline companion is scheming to kill them and steal their ship.
- Villain Protagonist: Prior to the arrival of the expedition, the story is told entirely from Coeurl's P.O.V. He's starving and slowly regressing into a nearly feral state as the last living thing on a dead, nameless planet, without even any other Coeurls to interact with. Even after the ship arrives and the human characters are introduced, van Vogt continues telling lengthy portions of Black Destroyer from Coeurl's viewpoint as he plots, with the humans essentially Hero Antagonists to his attempt to steal the ship and leave.