The Case of the Missing Cookie

Detective Dee put on her magnifying glass necklace. Mom had baked a plate of chocolate chip cookies. There were ten cookies on the plate. Mom went to answer the phone. When she came back, only NINE cookies were on the plate! 'Who took my cookie?' asked Mom. Detective Dee looked around the kitchen. She noticed three suspects: her brother Max, the family dog Biscuit, and her sister Lily. Time to find clues!