When their friends, Kami and Eddie Mark, accidentally fall into the time-travelling tunnels below Moose Jaw, fourteen-year-old Andrea and her ten-year-old brother Tony have no choice but to go back in time to rescue them. In that dank, dark underground, they learn of harsh working conditions being forced on Chinese immigrants, and Kami and Eddie are now among them! Can Andrea and Tony find enough money to pay the Chinese Head Tax the Canadian government has imposed on their friends? What risks must be taken to save Kami and Eddie and get safely back to the present?