Fifteen-year-old Beth Johnson is a talented and beautiful young actress. She is also a spy. Basking in the long, hot summer of 1666, Beth is looking forward to her first leading role. But when she receives an anonymous letter, the world is turned upside down for Beth and her friend John. Henry Vale, the dangerous mastermind behind the plots to kill the King, has kidnapped John's sister and is blackmailing John into helping him lure the King into a deadly trap. Will Beth and John be able to rescue his sister before the whole of London goes up in smoke?