The students of the 121 Express are infamous for bad behavior and Lucas knows his role on the bus will determine his social standing at his new school. Lucas is tired of being one of the nerds. When he attracts the negative attention of the cool troublemakers, he saves himself by teasing another kid. His ploy works and soon Lucas is right in the center of the mayhem on the bus. He loves his new found popularity, but when the fun and games push the bus driver to a nervous collapse and hospitalizes an elderly lady, Lucas begins to question his choices.
Trevor, Robyn and Nick decide they have a mystery to solve when Trevor discovers a suspicious looking young man snooping around. They learn about missing research involving the use of carob beans to aid in cancer treatment-potentially valuable information. With a shady looking grad student, a bitter activist and an employee of a medical research firm to deal with, our amateur sleuths are faced with their greatest challenge yet.