Marta, Tom and Lena had always liked a challenge, but what happened to them during their seaside holiday, none of them expected. The beach they went to every day was shrouded in mist, and at the end of it rose an old lighthouse, apparently abandoned for ten years. The townspeople whispered about strange sounds coming from inside it, but the children just laughed it off. Until. One evening, as they walked along the deserted beach, Lena noticed something disturbing. A light was flickering by the lighthouse, even though the electricity had been out for a long time. "Did you see that?" - she asked, rubbing her eyes. Martha, fascinated by puzzles, immediately offered to check what was going on. "Maybe someone's hiding in there or it's a .... a ghost!" - laughed Tom, but his voice was quiet. Armed with torches, they climbed the creaking stairs inside. There was silence in the dark corridor, broken only by the beating of their hearts. Suddenly, a quiet laugh rang out. "Did you hear that?" - whispered Marta. They approached the large metal doors leading to the top of the lighthouse. Someone had just gently swung them open. A faint greenish glow fell towards them. Lena reflexively took a step back, but the other two were already too intrigued to retreat. "Let's check it out!" - Tom said, embracing the torch more tightly. The door creaked open and a shadowy figure emerged from behind it, casting a brief, fearful glance at them. Suddenly the wind slammed the entrance behind them, cutting off their escape route. At the same instant, a new blinding flash appeared at the top of the lantern....