You can't mistake just anyone for a Phule.

When the planet Zenobia is invaded, Captain Willard Phule is made their military advisor. The first priority for Phule's Company: staying out from underfoot of the peaceful, dinosaurlike Zenobians . . .

But, unbeknownst to the Zenobians, they're getting two Phules for the price of one. A robot double of Phule appears out of nowhere. And only the real Phule knows who the real Phule is . . .