Septimus Warren Smith, aged about thirty, pale-faced, beak-nosed, wearing brown shoes and a shabby overcoat, with hazel eyes which had that look of apprehension in them which makes complete strangers apprehensive too.

Here, the narrator introduces Septimus. While walking with his wife, Lucrezia, down the street, Septimus overhears someone say that the prime minister sits in one of the cars. During this scene, he feels quite mad. Septimus is prone to bursts of anger, hallucinations, and nonsensical tirades, a result of shell shock from the war.

The world wavered and quivered and threatened to burst into flames. It is I who am blocking the way, he thought.

As Septimus reflects on the world and how he views himself, readers get a glimpse of how it feels to be Septimus, of how tenuous he holds onto life. He thinks everyone on the street is looking at him, and he feels terrified by his surroundings. He also feels rooted to the pavement, unable to move, until his wife hurries him along. Septimus’s story serves as the second plotline of the novel. His tale finally intersects with Clarissa’s story in the evening at her party.

“Look, look, Septimus!” she cried. For Dr. Holmes had told her to make her husband (who had nothing whatsoever seriously the matter with him but was a little out of sorts) take an interest in things outside himself.

While sitting in Regent’s Park with Septimus, Lucrezia tries to follow the doctor’s orders and points out an airplane drawing letters in the sky. In this scene, readers learn that Dr. Holmes does not consider Septimus’s condition to be physically debilitating. Instead, the doctor believes that Septimus can control his own madness by focusing on the world around him rather than on his own fears. Upon seeing the airplane, however, Septimus actually believes it is signaling to him.

But he began to talk aloud, answering people, arguing, laughing, crying, getting very excited and making her write things down. Perfect nonsense it was; about death . . . She could stand it no longer.

Here, the narrator explains how Lucrezia responds to Septimus’s odd behavior in public. Lucrezia and Septimus have been walking in Regent’s Park when his behavior becomes so extreme that his wife walks away from him for a while. When they return home, he seems more unhinged than ever. Although the doctors say there is nothing truly wrong with him, Lucrezia knows otherwise. He sees faces and flames and hears voices calling him horrible names. His behavior feels both frightening and abhorrent.

But the branches parted. A man in grey was actually walking towards them. It was Evans! But no mud was on him; no wounds; he was not changed.

Septimus’s recurring hallucination is attached to his past experience in the war. During the war, Septimus witnessed Evans, his friend, get killed. At first, staring into the trees, Septimus screamed at Evans not to come for he feared seeing the dead. Septimus can’t escape these horrible memories of the war. They haunt his present as well as his past. They are the source of his madness.

Lately he had become excited suddenly for no reason (and both Dr. Holmes and Sir William Bradshaw said excitement was the worst thing for him), and waved his hands and cried out that he knew the truth! He knew everything!

While sitting with Septimus in their home, Lucrezia sews a hat for a neighbor and recounts the details of Septimus’s illness. He has become increasingly detached from reality and descends into periods of unpredictable behavior and insane speech. He finds some things beautiful and others nonsense. He tells his wife to write down what he says as he speaks.

[T]he tears would run down his cheeks, which was to her the most dreadful thing of all, to see a man like Septimus, who had fought, who was brave, crying. And he would lie listening until suddenly he would cry that he was falling down, down into the flames!

Here, just before Septimus’s suicide, Lucrezia describes some of his unpredictable and wild actions. He reacts to common sounds outside as if he is hearing and seeing quite different things, such as drowning, flames, or music. He frightens his wife with his words, his behavior, and his threats of killing himself. He is spiraling out of control, and she watches helplessly.

“Must,” “must,” why “must”? What power had Bradshaw over him? “What right has Bradshaw to say ‘must’ to me?” he demanded.

Immediately after Lucrezia and Septimus have fun making the hat for the neighbor together, Septimus once again descends into his own madness when he remembers Sir William Bradshaw and his recommendations for treatment, which include separating him from his wife. He believes that the doctors will only make him worse, not better. He does not trust them at all. Lucrezia reminds him that he must leave because he has threatened to kill himself, but Septimus does not listen to her.

Holmes was at the door. “I’ll give it to you!” he cried, and flung himself vigorously, violently down on to Mrs. Filmer’s area railings.

Septimus declares his last words before killing himself. In this scene, Dr. Holmes has arrived at the Warren Smith home and is trying to get inside to see Septimus. Lucrezia stands in his way, unwilling to let him in, but he physically pushes her aside and enters. Earlier, Lucrezia hid the razors, thinking she was keeping Septimus safe. For a moment, Septimus considers using the bread knife but changes his mind. Instead, he throws himself out the open window.