Ancient Judea, more than 2500 years ago. A cruel enemy advances on the city of Yerushalayim. The righteous king Hizkiyau orders to cut a tunnel in the rocks, through which water will go to the city during the siege. Twelve-year-old Yonatan, who dreams of saving his hometown, also joins the ranks of the tunnel builders. Will Jonathan have the strength to work on a par with adults? Will the tunnel builders be able to complete the work on time? Will Jonathan be able to catch the enemy spy? How will the siege of Yerushalayim end? The extraordinary adventures of Yonatan take place against the backdrop of vivid pictures of life and life in Ancient Judea.