Kate, Anders, and Erik travel to Michigan’s Upper Peninsula where Kate’s Irish relatives live as caretakers of a mansion. Kate is excited to meet her cousin Megan, and it turns out that the two girls could be twins—except for one important difference. Megan is blind. Soon after their arrival, Kate, Anders, and Erik learn about a long-lost treasure map. But two shady looking people lurk in the darkness, and danger trails the four friends. Can they find the map in time? Act with courage in spite of fear? And will they escape the falling rocks deep within a copper mine? What becomes the biggest treasure of all?