"Moondog" of title is hero's pet - a creature found on the moons of Saturn, one who can give out electric shocks or even damage electrical equipment - hence useful as a weapon.
Tod Denver, hero, is near witness to a murder - murder of a prospector on moon who'd found a mine once worked by Martians & presumably still with enough treasures. That's how he gets the map of the treasure mine. Cops he reports murder to are in murderer's pay; so the bad guys are now after hero too!
Of course, all ends well - & hero is richer with a girlfriend too!
Fact sheet.First published: Planet Stories, July 1952.
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Related: Fiction set on moon.