Rivers sits in a corner, watching as Yealland brings Callan—a soldier who has lived through almost every major battle in the war—in to begin his treatment. Except for Rivers, the two men are entirely alone in the room. Yealland closes all the blinds so it is completely dark, aside from the glow of the battery and the reflection off Yealland's white coat and glasses.
Callan is brought in and strapped down to the chair. Rivers senses that the patient is frightened. Yealland attaches electrodes to the back of Callan's throat and continues to shock him repeatedly until he can make a sound. He shocks Callan for over three hours. When it seems like the patient is falling asleep, Yealland makes him get up and walk around the room. Callan tries to escape, but he cannot get out the door. It is locked from the inside, and only Yealland has the key. Callan considers attacking Yealland, but decides against it, and he submits to more electric shocks. To Rivers, the shocks seem extremely strong.
Yealland removes the electrodes from the back of Callan's throat and applies them to the sides of his neck. Callan seems to honestly be trying to speak, but only the sound "ah" comes out. Eventually, after many more shocks, Callan is stammering words. Yealland makes him feel completely powerless, repeating to him: "You must speak, but I shall not listen to anything you have to say." Finally, Callan is able to speak in full sentences. Yealland lets Callan up, and Callan smiles at him. Yealland does not like Callan smile, so he makes him sit down again, applies electrodes to his lips, and shocks him. When he gets up again, Callan no longer smiles. At the very end of the treatment, Callan must thank Yealland for curing him.
Rivers returns home that night, but finds himself unable to work or sleep. He is haunted by the images of Yealland and Callan, and the awful memories of the scenes of electro-shock therapy. He dreams of himself holding an electrode over a helpless patient's mouth, but the electrode turns into a horse's bit, and though he tries to push it into the mouth, it will not fit. Rivers wakes up screaming.
Rivers tries to understand his nightmare. He feels that the patient in his dream might have been Prior. Like Callan, he was mute upon arrival and seemed smugly satisfied with it. Rivers had used the tongue depressor on Prior in a moment of irritation with him. This makes Rivers wonder whether there is any real distinction between himself and Yealland. Both of them are in the business of controlling people, of making young men back into soldiers when they no longer want to be soldiers. Although Rivers prides himself on his more humane treatments, he nevertheless feels guilty for occasional pain he has inflicted on his patients.
Rivers realizes that what he witnessed that day was not the curing of the patient, but the silencing of one. By forcing Callan to speak, Yealland was forcing him to break, to relinquish his protest. It is then that Rivers realizes that the patient in his dream was not Prior, but Sassoon. Rivers confronts his guilt over breaking Sassoon, using his influence to force him to abandon his protest.