The Cosmic Computer — H. Beam Piper

Conn Maxwell told them: "There are incredible things still undiscovered; most of the important installations were built in duplicate as a precaution against space attack. I know where all of them are. “But I could find nothing, not one single word, about any giant strategic planning computer called Merlin!" Nevertheless the leading men of the planet didn't believe him. They couldn't, for the search for Merlin had become their abiding obsession. Merlin meant everything to them: power, pleasures, and profits unlimited. Conn had known they'd never believe him, and so he had a trick or two up his space-trained sleeve that might outwit even their fabled Cosmic Computer ... if they dared accept his challenge.