The Keep (1983) UK TV

In 1941, in Romenia, a German squad under the command of Capt. Woermann is assigned to protect a pass from a keep. Woermann notes that the fortress was built to prevent something to leave the interior and talks to the keeper Alexandru. He warns Woermann to not spend the night in the fortress and to not touch the crosses on the wall. However, two greedy soldiers decide to steal a silver cross, unleashing a smoke being and are murdered. When a fifth soldier is found dead in the keep, Woermann requests to be relocated with his men, but the SS Nazis under the command of the cruel Kaempffer arrive instead. He immediately executes three villagers, believing there are partisans in the village. Woermann stops him and shows a message written on the wall of the fortress. Kaempffer brings the local Father Fonescu to translate but he says that maybe Dr. Theodore Cuza, who is in a concentration camp, is capable to translate. The sick Dr. Cuza is brought in a wheelchair with his daughter Eva Cuza and says that the message is written in an ancient language that has been dead for five-hundred years. Meanwhile, a man in Greece named Glaeken, who seems to be possessed, travels by boat and motorcycle to the keep. What is the mystery of the keep?