A leisurely chapter-mystery in which an entire marching band and the bank president appear to be kidnapped--and the bank robbed--moments before the start of Springvale's annual Thanksgiving Day parade. The Dixon twins solve the case, as in Markham's The Halloween Candy Mystery (1982) and The Christmas Present Mystery (1984). Kate, who wants to be a scientist, and her sister Mickey, who wants to be a detective, figure out that Amos Amos, a lock salesman as well as bus driver for the Chatham Strutters, has only pretended to rob the bank to encourage Mr. Featherspoon, its president, to buy an Open Sesame Computerized Safe Lock from him. (The lock works by voice print and oral command: ""Open Sesame!"") To locate the band and its missing bus, Kate considers clues of weather and soil components while Mickey uses Holmesian deduction. Even though Amos Amos has barricaded Mr. Featherspoon in a closet because he ""didn't want (him) to see he wasn't robbing the bank,"" Mr. Featherspoon waives prosecution and all ends well. Duller and slower than it might be, but beginning readers discovering chapter books will probably read with interest to the end.