After saving the world again and returning home from 1999, Ethan Tate and Team Blackwoods have enjoyed a school year without robot drama. It's the summer before high school, and they're excited to reunite with Austin and Abby-now adults-at Big Woods Adventure Fun Camp.
As part of the fun, Austin and Abby plan a ghost investigation. An old lady living alone in a sprawling historical house claims to see her dead husband, though the team suspects she's just lonely and needs some company.
But when they visit the house, and an infamous madman from the 1800s mysteriously materializes with a Bowie knife and a murderous grudge, the group must confront a new reality. That reality gets even stranger when they start seeing robotic Skulleys in the long-abandoned gold mine on the property.
Some enigmatic force is merging science and superstition, giving life to things that need to stay dead. Ethan and his team are thrust into a desperate race to discover and stop it before another Fatal Error is unleashed. Yeah...adventure fun.