When 15 year old Ryn and his younger sister Aeden find themselves in Paris, France due to the murder of a distant relative, they cannot resist the temptation to travel back in time to find the killer. Although they think they have mastered Snell's Law of Refraction and a way to use light for time travel, something goes terribly wrong. The pair finds themselves in 18th century Paris a day before the storming of the Bastille and the start of the French Revolution. To make matters worse, they are lost in the underground sewers and their only hope of survival rests with a member of a secret society of revolutionaries who is bent on killing the aristocracy. When Ryn and Aeden learn that his next victim is their ancestor, who has sought refuge in the Bastille, they are forced to conceal their identities and find a way into that fortress to rescue the gentleman. With a bloodthirsty mob of angry citizens only hours away, Ryn and Aeden must rely on their instincts and skill to escape a frightening fate. Will time be their ally or their enemy?