In the mid-13th century, a Muslim army besieges the Castle of Caravaca, defended by the Knights Templar. Four knights manage to slip through the enemy lines with the mission of obtaining water for the besieged, but one of them, Guillermo, has a secret order to escape with the Holy Relic and keep it safe. At the crossroads between his duty to the Order and his loyalty to his brothers, Guillermo will be forced to choose: fulfill his hidden mandate and abandon his companions, or return with them to defend the castle until the end.