A group of friends, including the narrator and McKane, discuss the recent fame of Professor Sven Borgen, who has perfected brain grafting experiments on animals.
The narrator questions Borgen's mental state, but a stranger who overhears their conversation defends Borgen's genius and asserts the truth of the newspaper story.
The stranger claims to have personal knowledge of the experiments and shares a more detailed version of events.
According to him, the idea of brain grafting originated with another surgeon, Doctor X, who worked alongside Borgen for many years to achieve success.
Doctor X's son was severely injured and died, but before his death, he requested that his body be used for the brain grafting experiments...