Bruno is convinced that aliens are invading Dog City. Eliot decides to take this as a cue for this next Ace Hart Adventure.

Eliot sends Ace on a high-flying adventure to the moon to find out what happened to Arfstrong, the first mutt on the moon, who disappeared soon after he landed. Once there, Ace gets tangled in a web of espionage that includes Baron Von Rottweiler, Bugsy Vile and a cat named Bestov Breed. Ace races to save the moon from the clutches of the bad guys.