First published in Astonishing Stories (April 1940 issue), by Isaac Asimov. The crew of the Ceres has been tasked to explore Callisto, and discover why the seven other attempts had failed with no known explanations.
Ambrose Whitefield and Jenkins are grumbling to themselves about Jupiter, and the way it makes travel in the solar system so difficult. To stave off boredom, they decide to get drunk on the alcohol smuggled aboard by the captain, when they find a stowaway hidden within the cargo. Stanley Fields quickly becomes a favourite of the crew, listening to their stories about fighting off space pirates and exploring dangerous worlds.
Mac Steeden especially takes a shine to him, and tells Stanley about his travels with the legendary Captain Ethel. In fact, he still carries around Captain Peewee Wilson's old spacesuit as a memento. The crew convinces Steeden to gift the suit to the kid, and there's no more chance at boredom while the crew works to repair the suit enough to make it spaceworthy.
Once they've landed, matches are used to select which of the eight crewmen will go outside and investigate the Phobos; Captain Peewee Wilson's expedition ship. Jenkins, Charney, and Steeden are selected and go out in spacesuits, while Stanley presses his face against a porthole to watch them on their adventure. The Phobos is strangely damaged; covered by a soft white pulp, like slime from a giant slug. Both Steeden and Jenkins find bodies of the Phobos crew, but the bodies are both Stripped to the Bone, and the one outside is in a spacesuit covered by the same slime covering the ship.
They decide to send Jenkins back to Ceres when something disturbs the surface of a nearby lake; several four-feet wriggling monsters with a stalky growth glowing red are emerging in an apparent frenzy. The three spacemen try running back to their ship, but only Jenkins is able to get there, and barely him at that. Captain Bartlett realizes that these creatures are capable of manipulating magnetic fields, just like the Magnet Worm story. They must be responsible for the death of the seven previous explorations, and this ship is safe only because they have the brand-new beryl-tungsten hull, rather than the steel hulls that most ships have. Even their spacesuits involve large amounts of steel.
Chaney and Steeden must be left to die because the ship doesn't have any weapons to properly defend them, and going outside in a steel spacesuit is a guaranteed death. Stanley points out that his suit isn't steel; it's vitri-rubber.
"The Callistan Menace" provides examples of:
- Antagonist Title: The title refers to the mysterious danger on Callisto, one of Jupiter's moons. The menace is a creature, one to four feet long, with the ability to manipulate magnetic fields, using them to kill prey from a distance.
- Artistic License Astronomy: While the young Dr Asimov was aware that Callisto possessed a non-oxygen atmosphere, it is described with liquid water and plant-bearing.
- Author Vocabulary Calendar: The word "lugubriously" appears very out-of-place in this story where there are sparkling eyes and stolid grunting. A more smoothly incorporated word would've been mournfully or extravagantly.
- Character Narrator: The entire story is told from the perspective of Jenkins, an average crew member of the Ceres in their effort to find out what happened to the previous seven attempts to explore Callisto.
- Everyone Calls Him "Barkeep": The crew is under the command of Captain Bartlett, but since he's everyone's superior, he's only ever called by his rank (it's implied that the crew is a Navy spaceship, the Captain is the only one with rank).
- Extra-ore-dinary: Both the titular Menace and the Magnet Worm have Magnetism Manipulation that gets more powerful when magnetic metals (like lead and steel, but not rubber or beryl-tungsten composites) are nearby.
- Famed in Story: Captain Peewee Wilson is the most famous space explorer, and Steeden gets plenty of respect by association. Stanley loves listening to his stories the most, but treats each of the crewmates as if they were heroes straight from the dime spacer magazines.
- Featureless Plane of Disembodied Dialogue: Despite spending most of the time aboard ship, it's hardly described in any detail. There's apparently a lounge area separate from the cockpit, but characters seem to hold meetings everywhere but the airlock and personal quarters. No personal descriptions are given to identify the crew by sight, except for Mac Steeden's grey mustachio.
- First-Name Basis: All of the crew call Stanley by his first name because he's a young boy while even the greenest member of the crew has years of experience in space.
- Foreshadowing: Whitefield tells a story about Magnet Worms from Europa. They're little things (about six inches long) that can manipulate magnetic fields, giving them the power to kill from a distance. Knowing how the Magnet Worms work gives the crew a solution to the unnamed Callistan Menace.
- Genre Savvy: Stanley Fields, who stowed aboard their ship, loves "Dime Spacers"; mass-produced tales of adventure. These stories inspired Stanley to run away and stow aboard a spaceship without knowing their destination.
- Hold Your Hippogriffs: Most of the exclamations used in this story match the decade it was published, but a few idiomatic expressions have been used to establish this story takes place in The Future, such as "You bet all the radium on Titan" (instead of betting all the tea in China) or "pocket Lectronics" (instead of personal computers).
- Interplanetary Voyage: Half the story takes place on the way to Jupiter, letting us get to know the characters and setting up the tools needed to resolve the main conflict.
- Last-Name Basis: Because Stanley is still a kid, he calls everyone Mister and uses their last name, except for the Captain, who is only addressed by his role.
- Magnetism Manipulation: The Magnet Worm, found on Europa, is able to use magnetic fields to kill prey from a distance. Normally it can only affect creatures smaller than itself, but nearby magnetic metals increases the power, allowing it to kill larger prey.
- The Runaway: Stanley Fields ran away from his home on Ganymede to have space adventures "like they do in books".
- Solar System Neighbors: Callisto turns out to be inhabited by giant alien space slugs.
- The Storyteller: Stanley expects all of the crew to be able to tell him exciting stories about their adventures in the Solar System, but it's Mac Steeden that really enjoys stringing a tale together. He's acknowledged to have the best because he used to be crew for the legendary Captain Peewee Wilson.
- Stripped to the Bone: When the Ceres crew find the bodies of the Phobos, the clothes are left, but the flesh is partially or completely dissolved away to merely bone.