When Norobu finds a hole in the wall between his and his mother's rooms, he begins to use it to spy on her. To him, the hole offers a different perspective on the room than when he walks into it himself. He bursts into her room through the door and thinks:

Drab and familiar, the room bore no resemblance to the mysterious chamber he had seen through the peep- hole: it was here that he came to whine and to sulk - it's time you stopped coming into Mother's room so often with that excuse about wanting to watch the ships; you're not a child any more , dear - here that his mother would put aside her embroidery to help him with his homework while she stifled yawns, or would scold him for not tying his tie straight, or would check the ledgers she brought home from the shop...

He continues to use the peephole to spy on her, especially on days when she punishes him. He watches her at intimate times, including when her boyfriend Ryuji comes over and they make love.

Though Noboru likes Ryuji initially, his feelings change. At times, he finds him weak—even when this perceived weakness benefits him. Noboru lies to his mother and goes out with his friends to kill a cat. On the way back, he runs into Ryuji and has to ask him not to tell his mother that he wasn't where he said he would be. Noboru is disappointed in what Ryuji says, and thinks:

On top of that, Ryuji had said things he should never have said. "Small world, isn’t it? Have a good swim?" And when Noboru challenged the soaking shirt, he should have answered: "Oh, this? I rescued a woman who had thrown herself off the pier. This makes the third time I’ve had to go swimming with all my clothes on..."

But he hadn’t said anything of the kind. Instead he had offered this ridiculous explanation: "I took a little shower at the fountain up there in the park." And with that unwarranted smile all over his face!

Even though he agrees to keep Noboru's secret, this doesn't placate the child. He wants him to threaten him a little—to be more like Noboru's idea of a man and a hero. This eventually leads to Noboru deciding that he hates him after Ryuji finds the peephole and doesn't punish him.

He tells his friends what Ryuji is like. They all believe the world is empty and meaningless and that fathers are terrible. They decide that they need to take care of Ryuki on Noboru's behalf.

"That doesn’t mean we’re never going to," the Chief answered adroitly, his voice benign. "But getting back to Ryuji Tsukazaki," he continued, "he’s never meant much to the group as a whole, but for Number Three he was a person of considerable importance. At least, he’s credited with having shown Number Three some luminous evidence of the internal order of life I’ve mentioned so often. But then he betrayed Number Three. He became the worst thing on the face of this earth, a father. And something has to be done. It would have been much better if he’d just stayed the useless sailor he started out by being."

The boys ultimately lure him to the sea and drug his tea. They intend to do to him what they did to the cat; the story ends with Ryuji taking the cup of tea and swallowing the bitter liquid inside.