It’s the time of the Crusades, and Christian forces in Acre are all too aware that an attack from Muslim armies may be just around the corner. There are certainly no guarantees that the Christians will hold onto the Israeli city, either, despite the fortifications they have built up. So, one of the Crusaders’ military orders, the Knights Templar, decide to build themselves a secret escape: a passage beneath the bowels of Acre that leads in turn to the ocean. And the tunnel itself is so well concealed that it ultimately remains undiscovered for 700 years…