"Mitkey Rides Again" (1950) by Frederic Brown

If you liked Frederic Brown’s superb story The Star Mouse about the rocket scientist Professor Oberburger and his precious and very precocious mouse-assistant Mitkey – and how could you not have liked/loved it? – then you will want to catch up on the later adventures of Mitkey and his Minnie published in the November 1950 issue of the magazine Planet Stories, whose striking cover by Allen Anderson and several story illustrations by Herman Vestal are all included here.

(8,000 words)

An ebook is available for downloading below.

For Those Who Did Not Read Mitkey’s Adventures in "THE STAR-MOUSE":

MITKEY, a small gray mouse, is captured by Professor Oberburger, a refugee German scientist living in Connecticut and working on a rocket to be sent to the moon. Mitkey is placed in a compartment of the rocket, for experimental purposes.
The rocket is deflected by, and lands on, Prxl—an asteroid with a highly eccentric orbit. It is inhabited by a race of tiny but super-intelligent beings.
The Prxlians, in order to question Mit­key, raise his intelligence level to the point where he can assimilate and understand his own memories and tell them about con­ditions on Earth.
Thus Mitkey finds himself with a lan­guage—the thick German dialect spoken by the professor, who had talked inces­santly to himself and to Mitkey while lie worked on the rocket.
The Prxlians, who became fond of Mit­key, send him and the rocket back to Earth. Mitkey approaches Professor Oberburger and tries to sell him on the idea of letting Mitkey raise the intelligence level of all other mice, by means of a ray pro­jector which the Prxlians have taught him how to construct.
Mitkey believes intelligent mice could live in peace with men, and suggests that mice be given a portion of the earth as their own. The professor is doubtful.
But an accidental electrical shock spoils Mitkey’s plans.
The professor has been keeping Minnie, Mitkey’s mate, as a pet, on an ’island’ surrounded by an electrical barrier. Mitkey, seeing Minnie there, dashes recklessly across and receives the shock which de­stroys his new-found intelligence and makes him again just an ordinary little mouse.
And he and Minnie resume their happy life behind the wall of the professor’s lab­oratory, until . . .

Mitkey Rides Again (e-book)