Basia and Franek spent the whole afternoon in the garden under the big, spreading apple tree. They decided to build their own tree house. They brought a ladder, a hammer and some old planks. They laughed, tapped the hammer and planned where the window would be and where the secret entrance would be. When the cottage was almost ready, it got a little darker. The sun was going low and mysterious sounds began to rustle in the leaves. Basia looked down and suddenly saw something strange - a shadow had moved under the tree, as if someone or something was hiding there! - Franek, did you see that? - she whispered frightened. Franek looked down and trembled with emotion. The shadow moved slowly and something rustled quietly in the grass. The friends froze in stillness, looking deep into the garden. Then suddenly there was a quiet sound: "shur, shur..." Basia and Franek held their breath. Would they dare to find out who or what was hiding under their cottage?