The Key is a mystery short story by Isaac Asimov
A standalone story, it was first published in the October 1966 issue of The Magazine of Fantasy and Science Fiction. It was later collected in 1968's Asimov's Mysteries.
Summary[]
On the Moon, an extraterrestrial artifact is hidden, capable of amplifying and transmitting thoughts to the point of damaging another person's mind. Two explorers, Jennings and Strauss, discovered it. Jennings is now dead from a stab wound inflicted by Strauss, who has been driven insane.
The investigation into the artifact's location is hampered because the only clues are a piece of paper with cryptic symbols found in a spacesuit gauntlet and the ravings of the insane Strauss, who is a member of the eugenicist "Ultras" society. It is feared the Ultras could use the device to eliminate most of humanity. The original paper has been stolen, leaving only a copy.
One clue on the paper is a vertical arrow pointing to the astrological symbol for Earth. An investigator realizes this means "go to Urth," a reference to extraterrologist Wendell Urth, whom Jennings had studied under.
When contacted, Urth analyzes the clue and Strauss's recordings. He determines the symbols are deliberate red herrings. He explains that Jennings, who enjoyed bad puns, used the artifact's power to create a bilingual pun. Strauss repeatedly called the artifact "the key." Urth connects this to the word "clue," which sounds like "Klau," the surname of astronomer Christof Klau. Klau's Latinized name is Clavius, which derives from the Latin word "clavis," meaning "key." Therefore, the "clue" points to the "key," and the artifact is hidden in the lunar crater Clavius, at the point where Earth is directly overhead.
Urth also concludes that the Ultras cannot use the artifact, as it requires a capacity for empathy, a quality the coldly rational Strauss and his fellow Ultras lack.