Andalusia, 1938. The Spanish Civil War is coming to an end. A handful of communist Stalinists, driven by the enemy - the Spanish fascists - into a small town, take hostages and lock them in a beautiful old cathedral. The Communists plan to blow up the temple, destroying as many enemies as possible. It seems that the imprisoned people do not have the slightest chance to survive, but one of them, the former minister and connoisseur of the Middle Ages, Professor Pinson, gets his hands on the manuscript of a Jewish alchemist, stored in an 11th-century mosque hidden under the cathedral. And this book gives people the key to freedom; true, not everyone will be able to enjoy it...