It's 1952 and fourteen-year-old Janie is shocked to learn that her television writer parents are communist sympathizers. They must flee from California to London in a week's time. Once in London, she encounters an apothecary whose shop is across the street from Janie's apartment. His son, Benjamin, goes to her new school. As the two are playing chess in the park, they see Mr. Shishkin(who works for the Soviet embassy) meet the apothecary and give him a secret message. The teens follow the apothecary back to the shop where Benjamin decides to confront his father about his clandestine meeting. Just as they are about to get some answers, men break in and the apothecary shoves the two in a cellar and entrusts his son with a book that has been in the family for over 700 years, the Pharmacopoeia. He warns, "No police! I need you to protect the Pharmacopeia and keep it safe." From that moment on, the two embark on an adventure to find Benjamin's father, decipher the Pharmacopoeia, rely on some espionage of their own, set out on a crazy adventure, try secret potions and save the world.