Sally's father bans her from detective work. She disobeys him, however, and investigates a mysterious cockroach thief, with Doowee's assistance. Sally's father is looking for picket picketer.
After three windows are broken at school, the Principal's son asks Sally to investigate. However she questions his intentions when she learns the Principal has already found the culprit. They later discover that the principal's son is a secret skateboarder and the boy principal caught was outside school campus skateboarding with the principals son.
A very pretty girl, Sinitta, is accused of stealing sweets at a modern art museum, and she wants the SBI to prove her innocence. Sally does not trust Sinitta and does not want to take the case, but Dowee is charmed by the pretty girl, and insists that they investigate. It turns out that Sally was right : the case is a trap set by Sinitta's uncle, who wants to get Harry off his case.
Sally and Doowee discover that they are not the only detectives solving crimes anymore. There's a new detective agency on the block and its bigger and better at solving the crimes. Who is Mr Big? Will he ultimately bring the SBI to a complete stop and break apart the friendship that Sally and Doowee share? In the end will this rival go so far as to make one hurt the other?.....
