The Mysterious Cache is the third book in a trilogy. It follows The Mysterious Firefly which followed The Mysterious Icicle.

Pandora High School is back from summer vacation. The gang of seven are looking forward to homecoming activities. They are hoping that the new year will be free of the dramatic episodes that they were drawn into during the spring and summer.

The narrative begins with Heather finding her bedroom in total chaos, thanks to her little sister's new dog. Lizzie was not honoring her promise to their parents to watch her Portie, Smudges. To top it all off, Heather will be stuck walking the dog since her sister has been grounded for two weeks. Little does she know that the chore will lead the gang into more intrigue.

Read along to see how the friends decide to handle the situation they find themselves facing. Have they learned anything from the previous two dilemmas that will affect their decision-making?