John Brunner’s 1980’s The Infinitive of Go is a standalone science fiction novel.
Cold War paranoia provided the funds to finance Justin Williams and Cinnamon Wright’s revolutionary teleporter. The “poster,” as the device is innocuously dubbed, seems to work perfectly. Preliminary tests show that inanimate and animate payloads arrive intact.
The first long-range human test seems to have gone perfectly until courier George Gunther demands a countersign. Since no such countersign had been arranged, it cannot be given. Gunther immediately kills himself while destroying the documents he was conveying.
Something has clearly gone wrong, but what?