The fifth story in the New York Times bestselling Questioneers chapter book series following Ada Twist, Scientist and friends Blue River Creek has a problem: there's a pet thief on the loose! Or at least, Sofia and Iggy are convinced that there is once their pets go missing. But as a scientist, Ada knows it's important not to jump to conclusions and to follow the facts. How will they find out what really happened to the town's pets? By using the scientific method, of course! Through making a hypothesis, collecting data, and experimentation, the Questioneers must find the missing animals before even more pets disappear! Watch the Questioneers in the Netflix television series Ada Twist, Scientist! Check out all the books in the Questioneers series: The Questioneers Picture Book series: Iggy Peck, Architect . Rosie Revere, Engineer . Ada Twist, Scientist . Sofia Valdez, Future Prez . Aaron Slater, Illustrator . Lila Greer, Teacher of the Year . Billie Jean Peet, Athlete The Questioneers Chapter Book series: Rosie Revere and the Raucous Riveters . Ada Twist and the Perilous Pants . Iggy Peck and the Mysterious Mansion . Sofia Valdez and the Vanishing Vote . Ada Twist and the Disappearing Dogs . Aaron Slater and the Sneaky Snake . Lila Greer and the Shrieking Shadow Ada Twist, Scientist: The Why Files series: Exploring Flight! . All About Plants! . The Science of Baking . Bug Bonanza! . Rockin' Robots! . TeamGreen! Questioneers: Ada Twist, Scientist series: Ghost Busted . Show Me the Bunny . Brainstorm Book . 5-Minute Ada Twist, Scientist Stories The Questioneers Big Project Book series: Iggy Peck's Big Project Book for Amazing Architects . Rosie Revere's Big Project Book for Bold Engineers . Ada Twist's Big Project Book for Stellar Scientists . Sofia Valdez's Big Project Book for Awesome Activists . Aaron Slater's Big Project Book for Astonishing Artists