At the center of this third book in the Secret series is the Tuning Fork and its mystery. Cass, Max-Ernest, and Yo-Yogi find themselves involved in a great “chocolate” mystery. Sinister Señor Hugo, great experimenter of chocolate, and the infamous Dr. L and Ms. Mauvais hold Cass’ mom as hostage as they seek the secret of immortality. Bosch again intersperses the story with warnings for readers and gives footnote explanations about types of chocolate. Ford’s hauntingly humorous illustrations provide brief intermissions in the story. Although there is no secret code to unravel, fans of the first two books will find this sequel satisfying. Grades 4-7.