Thirteen-year-old Erin jumps at any chance to go geocaching — using GPS technology to locate hidden caches. But family outings seem as likely as finding a cache in an active volcano after Erin's unemployed dad relocates to another state. When her parents then stop talking to each other and they lose their house, Erin feels about as secure as a fault line during an earthquake.

Setting out with her friend Dev, Erin discovers a mysterious note inside a geocache. Convinced it leads to valuables that could help her family, she and Dev track down geocaching clues. Besides cryptic messages, they face secret tunnel networks, gobs of chewed bubblegum, and woods bristling with vengeful wasps. Chess team bullies, scheming geocachers, and self-doubt also threaten their mission.

Meanwhile, Erin's dad extends his remote stay, and financial worries take up permanent residence at home. Will Erin and Dev unravel the mystery before her family falls apart?