Invited by the New Commandant of a penal colony, a worthy and esteemed Traveller meets with an Officer to hear about the workings of a mysterious apparatus. They meet in the middle of the blazing hot desert, accompanied by a Soldier and a Condemned Man.
The Officer is deeply proud of the apparatus and relishes explaining how it works to the Traveller. He shows him the three parts—the Bed, where the Condemned Man will lie down; the Inscriber, which has the law the Condemned Man broke loaded into it; and the Harrow, consisting of needles that inscribe the message into the body and then shoot water out to wash away the blood. For the first six hours the person in the machine feels only pain, but after the sixth hour they begin to think about what is being written on their body, and they ultimately achieve a sort of transcendence. By the twelfth hour, they die and their body is dropped into a pit beside the apparatus.
The Officer also explains that the criminal sentences in the penal colony are levied without the accused having a defense; the assumption is that they are guilty. For example, the Condemned Man was supposed to be a sentinel in front of a Captain’s door and salute him every hour, but once when the Captain looked outside the Condemned Man was asleep. The Captain reported the man and thus the Officer judged him guilty. The Officer says that it saves everyone time because no doubt the Condemned Man would have lied and things would have been protracted and wearying.
The Condemned Man was not told of his fate, though, and does not know why he is currently here, tied up and watched over by the Soldier. The Traveller is disconcerted as he watches the infantile and brutish prisoner look upon the apparatus with mild curiosity rather than fear. He begins to think that apparatus is unjust.
The Officer, having completed his inspection of the apparatus and the extolling of its merits, has the Soldier strap the Condemned Man into it. The Officer explains that he is the last advocate of the use of the apparatus. Both were the creation of the Old Commandant, now deceased. The Officer glows when he speaks of this brilliant man and how back in his day, the torture was a popular public spectacle. Now, though, the New Commandant has professed his dislike of the procedure. The Officer thinks that the Traveller was invited to see the apparatus with the expectation that he would disapprove of it, giving the New Commandant the outside backup he needs to rid the penal colony of the apparatus and the archaic justice system altogether.
The Officer implores the Traveller instead to speak on his behalf and to defend the apparatus. He need not even come out emphatically for it, the Officer explains; he should just not voice any objections. The Traveller says he cannot do that. The Officer sees that the Traveller will not change his mind and orders the Condemned Man be released. The latter is visibly shocked but gleeful.
The Officer then fixes a new message onto the Inscriber, “Be Just,” and removes his clothes. He lies down on the Bed and the Soldier and Condemned Man strap him down. The Traveller knows what will happen and feels that he cannot interfere.
The apparatus is turned on, but very quickly it begins to break down; it is not at all as harmonious and smoothly-functioning as the Officer implied. Gears begin to tumble off, and the needles do not move around lightly but instead stab the Officer. The water does not come out, so the blood does not wash away. When the apparatus stops, the Traveller peers at the Officer. The Officer’s body is horribly mutilated, a needle has gone straight through his forehead, and there is absolutely no look of transcendence on his face.
Back in the colony, the Traveller visits the hidden gravesite of the Old Commandant. A plaque says one day the Old Commandant will return and his followers will rise up.
The Traveller prepares to leave the colony. The Condemned Man and Soldier try to jump on his boat to flee as well, but the Traveller brandishes a heavy rope at them and leaves them on the shore.