By the end of Monday, Lulu had learned to disguise herself as anyone and anything. She had also learned to notice all the little mistakes and carelessnesses that would tip her off when someone else was disguised. On Tuesday, Lulu’s class would be taking a field trip to a museum, encountering many people during the day. Lulu’s spy assignment was to figure out which of these people were actually an in-disguise Ms. Solinsky.