As young Canadian soldier Dick prepares to leave home to fight in the First World War, his mother reminds him that he is going to fight for honour and principle, and urges him not to do anything that he couldn't admit to his sister or mother.

Outside the National Gallery in Trafalgar Square, Dick is accosted by a prostitute. A passing Canadian officer interrupts, and warns Dick of the risks that he is taking. He gives him a card with the address of a doctor. He shows the officer a photograph of his fiancée, who turns out to be the officer's sister Jane.

Dick visits Dr. Burns, who shows him around hospital wards occupied by victims of venereal disease at every stage, including rotting legs and hands. The 'Final Report of the Commission on Venereal Diseases' explains that hereditary syphilis leads at an early age to blindness and deafness. The disease's germs, threadlike bodies seen under a microscope, attack healthy corpuscles, forming syphilitic sores seething with bacteria.

Dr. Burns directs Dick to the nearest school for the blind. More than half the children there contracted blindness as a result of hereditary venereal disease.

When the war ends, Dick's brother Tom, who spent the war years consorting with prostitutes in London (and being robbed) returns to Canada, where his wife falls ill. The doctor discovers that she has been infected with syphilis. Tom confides in Dick, who urges him to undergo a cure.

The cure is successful, and Tom returns home to see his baby for the first time (it was born during his absence). On discovering that the child has been born blind, Tom is overcome with despair.