The story begins with Hank Morgan, a practical and modern-day (19th century) engineer from Connecticut, who is suddenly transported back in time to the medieval era, specifically to the time of King Arthur's court. Hank, who becomes known as "The Boss" due to his knowledge and inventions, finds himself in a land of knights, castles, and magic.

Hank's practical and scientific mindset clashes with the superstitious and medieval world he now inhabits. He uses his knowledge of science and technology to introduce innovations and reforms in King Arthur's kingdom. He attempts to modernize the society by implementing things like telegraph lines, factories, and schools.

However, Hank's efforts to bring progress to the kingdom are met with resistance from traditionalists and religious authorities. His attempts at reform and modernization often lead to unintended consequences and conflicts.

Throughout the novel, Hank faces various challenges, including his interactions with historical figures like Merlin and his efforts to change the course of history. He also becomes romantically involved with a woman named Sandy, who becomes his ally in his quest for progress.