Kuba, Lena and Maks were sitting on the wall in front of Kuba's house, eating pistachio ice cream. It was a hot August afternoon and yellow heat was pouring from the sky. The smell of freshly cut grass was in the air, and somewhere in the distance came the lazy clatter of a tractor. It was one of those days when it seems that nothing out of the ordinary can happen. But then Lena stated: - Hey, did you hear that? The boys stopped talking and listened. And then they heard it, too: a quiet, strange sound, something between a droning whistle and the rustling of leaves. It was coming from the abandoned Green Manor, which stood on a hill just beyond their street. - 'Probably the wind,' muttered Kuba, but he didn't sound too sure. - 'Or ghosts,' whispered Maks with feigned fear. Lena only smiled. She was the bravest of the three and was always the first to take on new challenges. - 'Maybe there's someone out there? - she suggested. - Let's check it out! The friends set off along the path between overgrown bushes that led to the Green Manor. Up close, the house looked even gloomier than from the street: the windows were boarded up and tall nettles grew right up to the threshold. After a while, however, Lena found where one of the boards was loose. - Come on, this way in! - she whispered. They squeezed inside one by one. Inside there was a chill and a pleasant smell of old books mixed with dampness. Shadows danced on the dusty walls and the sun's rays came through the cracks. Suddenly, the boys and Lena heard the same sound again, but much louder than before. It was coming from behind the door leading to the cellar. - What could it be? - whispered Maks, squeezing Kuba's sleeve. Lena was already holding the handle. After exchanging glances, the friends walked closer. When Lena pressed the door, it creaked and swung open slowly. A soft green light came on on the stairs leading deep into the basement, and the sound intensified further. Kuba took a step forward, Lena right behind him, Maks held his breath. They looked down and saw....