Jim Floyd serves as the technical assistant to the eccentric Professor Breckenridge in the early 20th century setting of Bristol, England. He occupies a rented room above the Ten-Kai Tavern, a Chinese restaurant run by a young woman named China, who also acts as his landlady. Floyd is depicted as a brilliant but sweet-natured and somewhat reserved young man, whose quiet dedication to his scientific work often contrasts with the boisterous impracticality of the professor. His primary motivation is a deep and sincere affection for China, though he is characteristically unable to openly express his feelings for her.

Floyd's role in the story is largely defined by his relationship with China and his contributions to the professor's extraordinary projects. He is a diligent worker, often tasked with turning Breckenridge's wild theories into functional reality. A central part of his personal journey involves completing a gravity disrupter device that had belonged to his missing father. Floyd’s scientific aptitude is not merely a profession but a means of expressing his love. He is capable of engineering feats that blend romance with science fiction, most notably his plan to literally carve a message for China onto the surface of the moon. This grand gesture exemplifies his character: a man who, despite his personal shyness, can conceive of and execute impossible romantic acts through his intellect and skill. His key relationships are with the professor, his mentor and employer, and with China, whose affection he reciprocates but with whom he struggles to connect on an emotional level, leading to a gentle tension in their daily interactions.