The Brain Sinner by Alan Edward Nourse

As if a dam had broken, the reports began streaming in. Three more came from Chicago. Then a call came from Cleveland, from a Psi-High technician there who was not remotely connected with the Federal Security Commission. Then from Pittsburgh, then New Philadelphia. Like a fearful, ominous flood the reports of the Alien's contacts swarmed in. And Paul Faircloth and Jean Sanders were ready for them.

Their headquarters was a small suite of rooms in a middle class residential hotel in the heavily populated metropolitan area between Washington and Baltimore. Few of the Federal Security agents, Psi-High or otherwise, knew this. They knew only a visiphone priority code number, and a special word-key for scrambling. This was as Faircloth insisted. Of all the agents posted and assigned, only Paul, Jean, and Roberts knew the true nature of the operation, and each of them worked out their own illogical details without telling the others.