In a desperate attempt to escape another "lesson" (bullying session) from Jake "the Snake," Mouse and his friends Shelby and Lucy take shelter in the old, supposedly haunted, Holsom barn. When one of Jake's friends, Jorge, discovers them hiding in the barn's silo, a scuffle breaks out and a hidden button is accidentally pressed. Suddenly the silo floor descends like an elevator!

Once the elevator stops, our gang makes their first discovery: Horatio Holsom, the eccentric old inventor who disappeared over forty years before, built an enormous underground laboratory below his family's farm. The place is packed with incredible gadgets, but only Mouse—a near genius with computers—is interested in staying. The elevator seems broken, and Jorge is still intent on roughing up Mouse. Their arguments are interrupted by a cold, metallic voice. The four kids learn they are not alone in the compound.