All Cats Are Gray by Andre Norton - An odd story, made up of oddly assorted elements that include a man, a woman, a gray cat, a treasure—and an invisible being that had to be seen to be believed.
Steena of the spaceways—that sounds just like a corny title for one of the Stellar-Vedo spreads. I ought to know, I’ve tried my hand at writing enough of them. Only this Steena was no glamour babe. She was as colorless as a Lunar plant—even the hair netted down to her skull had a sort of grayish cast and I never saw her but once draped in anything but a shapeless and baggy gray space-all.
Steena was strictly background stuff and that is where she mostly spent her free hours—in the smelly smoky background corners of any stellar-port dive frequented by free spacers. If you really looked for her you could spot her—just sitting there listening to the talk—listening and remembering. She didn’t open her own mouth often. But when she did spacers had learned to listen. And the lucky few who heard her rare spoken words—these will never forget Steena.
She drifted from port to port. Being an expert operator on the big calculators she found jobs wherever she cared to stay for a time. And she came to be something like the master-minded machines she tended—smooth, gray, without much personality of her own.
But it was Steena who told Bub Nelson about the Jovan moon-rites—and her warning saved Bub’s life six months later. It was Steena who identified the piece of stone Keene Clark was passing around a table one night, rightly calling it unworked Slitite. That started a rush which made ten fortunes overnight for men who were down to their last jets. And, last of all, she cracked the case of the Empress of Mars.
