The book opens with the youthful diary of W.N.P. Barbellion, an intensely egotistical and observant schoolboy in rural England who develops a passionate fascination for natural science. He records his rambles, bird-watching, egg-collecting, and early botanical and zoological dissections with fervent delight, revealing a mind deeply attuned to the beauty of the English countryside.
As Barbellion grows into early adulthood, the narrative darkens with the realization of his straitened financial circumstances and his chronic ill health. Bound to the drudgery of newspaper reporting to support his family, he struggles constantly against poverty and lack of formal scientific training, yet drives himself forward to master chemistry, German, and advanced comparative anatomy.
After years of relentless effort, he secures a coveted post as an assistant at the Natural History Museum in London. However, this professional triumph coincides with the definitive onset of severe physical decline, marked by heart disease and escalating symptoms of multiple sclerosis. He faces the terrifying prospect of physical degeneration with a mixture of bitter irony, fierce rebellion, and intellectual hunger.
Throughout his decline, Barbellion continues his microscopic studies, engages in complex personal relationships, and confronts the absolute finality of death. He documents his changing attitudes toward love, ambition, and human companionship with merciless honesty and psychological precision, refusing to sink into passive resignation.
The narrative follows his tempestuous romance, his marriage, and his desperate race against time to complete his private journals and scientific papers. The author maintains his critical, observational stance toward his own failing body and mind until the very end, viewing his fate without sentimentality while preserving a fierce zest for life.