Readers can explore engineering concepts such as artificial intelligence, engineering design, and engineering ethics in this young adult mystery. Seven-year-old Maddie Reyes can talk to Mom, Dad, and 14-year-old Sadina, her sister and protector. But with the rest of the world -- except for Bella, her robotic cat -- she's too terrified to speak a word. Maddie wakes one night to find an intruder in the house, and now she's the only one who can identify him and save Mom from being arrested. Sadina suspects her best friend, Rio -- especially now that Rio has started paying attention to another girl. With Mom in trouble and Rio acting like a stranger, Sadina's world is collapsing. And that's when her friends join together to help transform Bella into Chattercat, a talking robot that just might get some answers from Maddie.