So appalled

It was a dreadful pity. For that made Septimus cry out about human cruelty - how they tear each other to pieces, The fallen, he said, they tear to pieces. "Holmes is on us" he would say, and he would invent stories about Holmes; making himself roar with laughter or rage, for Doctor Holmes seemed to stand for something horrible to him. "Human nature," he called him.

Desperately suffering from his post-traumatic stress disorder, Septimus has an entirely different perspective on life after his war experience. Septimus has been subjected to the worst that humanity has to offer. He has been exposed to not only the physical violence of war, but also its aftermath. Septimus has suffered mentally, having to live with the memories of the fighting; as well as emotionally, constantly having hallucinations of his dead comrades, being driven to insanity by the guilt of surviving while all his friends had perished.

Septimus comes to the realization that people are the cause of his anguish: the militants he has had to fight against, the people in his country that he has had to fight for, and his dead comrades that he has had to fight with. Septimus then manifests this frustration for humanity in Doctor Holmes. It is interesting how Septimus creates this entity to seem so benign yet so malevolent at the same time.  Inventing stories that create uproarious laughter,  Septimus does battle with Holmes constantly. He battles the good-natured, almost foolish doctor, because he knows that the doctor is responsible for all of his suffering. Septimus, as the fallen, tries to pick up his torn pieces.