It is 1752 and seventeen-year-old Agnes Trussel arrives in London pregnant with an unwanted child. Lost and frightened, she finds herself at the home of Mr. J. Blacklock, a brooding fireworks maker who hires Agnes as an apprentice. As she learns to make rockets, portfires, and fiery rain, she slowly gains his trust and joins his quest to make the most spectacular fireworks the world has ever seen.