In Lessing's "Through the Tunnel," Jerry, a young English boy, and his mother are vacationing at a beach they have come to many times in years past. Though the beach's location is not given, it is implied to be in a country that is foreign to them both. Each tries to please the other and not to impose too many demands. The mother, who is a widow, is "determined to be neither possessive nor lacking in devotion," and Jerry, in turn, acts from an "unfailing impulse of contrition—a sort of chivalry."

On the second morning, however, Jerry lets it slip that he would like to explore a "wild and rocky bay" he has glimpsed from the path. His conscientious mother sends him on his way with what she hopes is a casual air, and Jerry leaves behind the crowded "safe beach" where he has always played. A strong swimmer, Jerry plunges in and goes so far out that he can see his mother only as a small yellow speck back on the other beach.

Looking back to shore, Jerry sees some boys strip off their clothes and go running down to the rocks, and he swims over toward them but keeps his distance. The boys are "of that coast; all of them were burned smooth dark brown and speaking a language he did not understand. To be with them, of them was a craving that filled his whole body." He watches the boys, who are older and bigger than he is, until finally one waves at him and Jerry swims eagerly over. As soon as they realize he is a foreigner, though, they forget about him, but he is happy just to be among them.

Jerry joins them in diving off a high point into the water for a while, and then the biggest boy dives in and does not come up. "One moment, the morning seemed full of chattering boys; the next, the air and the surface of the water were empty. But through the heavy blue, dark shapes could be seen moving and groping." Jerry dives down, too, and sees a "black wall of rock looming at him." When the boys come up one by one on the other side of the rock, he "understood that they had swum through some gap or hole in it ... [But] he could see nothing through the stinging salt water but the blank rock." Jerry feels failure and shame, yelling at them first in English and then in nonsensical French, the "pleading grin on his face like a scar that he could never remove."

The boys dive into the water all around him, and he panics when none surface. Only when his count reaches 160 do the boys surface on the other side of the rock, and as soon as they come up, they leave. Believing they are leaving to get away from him, he "cries himself out."

When Jerry sees his mother that afternoon at the villa, he demands that she buy him goggles immediately. With the goggles he can suddenly see, as if he had "fish eyes that showed everything clear and delicate and wavering in the bright water." He descends again and again desperately trying to find the opening in the rock that the older boys had swum through, until finally "he shot his feet out forward and they met no obstacle."

Jerry is determined to be able to swim through the tunnel, and begins immediately a practice of learning to control his breathing. He lies "effortlessly on the bottom of the sea" with a big rock in his arms and counts. That night his nose begins bleeding badly, and he spends the next two days exercising his lungs "as if everything, the whole of his life, all that he would become, depended upon it." When his nose bleeds again, his mother insists that he rest with her on the beach. He does so for a day, but then the next morning he goes off to the bay by himself without asking, "before his mother could consider the complicated rights and wrongs of the matter." He again practices holding his breath under water, and he experiences a "curious, most unchildlike persistence" while studying the tunnel.

When his mother announces they are to leave in four days, Jerry vows to succeed in his quest even if it kills him. His nose bleeds so badly he becomes dizzy, and he worries that the same might happen in the tunnel, that he really might die there, trapped. He resolves to wait until the following summer, when he will be bigger and stronger, but then an impulse overtakes him and he feels that he must make his attempt immediately—now or never. "He was trembling with fear that he would not go; and he was trembling with horror at the long, long tunnel under the rock, under the sea."

Once inside the tunnel he begins counting, swimming cautiously, feeling both victory and panic. "He must go on into the blackness ahead, or he would drown. His head was swelling, his lungs cracking ... He was no longer quite conscious." Even when he surfaces, he fears "he would sink now and drown; he could not swim the few feet back to the rock." When he finally pulls himself onto the rock and tears off his goggles, they are filled with blood.

He rests and then sees the local boys diving half a mile away, but he is no longer interested in them. He wants "nothing but to get back home and lie down." His mother is concerned at his "strained" appearance when he returns to the villa, but consoles herself remembering that "he can swim like a fish." He blurts out that he can stay under water for "two minutes—three minutes, at least," and she replies in her usual moderate way, cautioning him that he "shouldn't overdo it." Jerry has succeeded in his quest—it is "no longer of the least importance to go to the bay."