'Someone has taken something from the principal's office at school! Who would have done such a terrible thing? And when one of Billie's friends becomes a suspect, will Billie even know who to trust anymore?' (Publication summary)
'Billie and the Secret Mystery Club have been given a very important mystery to solve for the principal at school. A long time ago, a time capsule was hidden in the school somewhere, and it's up to the SMC to find it!' (Publication summary)
