Ola sat on a low wall under a maple tree that grew just beyond the wall of their townhouse. The sun illuminated a torn notebook and the shadows of the leaves danced across the pages as she tried to think of a topic for a Polish story. The tenement she lived in looked like all the others: grey high walls, creaking stairs, knocked-out tiles in the courtyard around which cats and pigeons were having their little wars. Lately, Ola had felt that everything was predictable. Homework, conversations on Messenger, arguments with her younger brother over the remote control. Routine. A daily routine that sometimes weighed her down like a heavy backpack after P.E. lessons. But today, as she dropped her backpack under a tree, she saw something unusual: a small yellow envelope wedged between the roots of a maple tree. For a moment she looked at it with distrust. Maybe someone had lost the letter? Maybe it was some junk mail? But the envelope was too clean, clearly new, and on the back was a drawing - a key and a round magnifying glass drawn in purple marker. Ola cursed in her mind at her curiosity and reached for the find. Inside there was no address, but a piece of paper with even, neat handwriting: "Hi, if you are reading this, it means you are able to see more than others see. Maple is a place where the world is intertwined with something not obvious. If you have the courage, come back here at dusk. Trust what you hear or feel. This is just the beginning." Ola looked around. Everything seemed ordinary. Children on their bikes, a neighbour walking her dog. And yet she felt something begin to vibrate just below the surface of everyday life. Her heart beat faster. Walking home, she kept thinking about the letter. Who was the author? And what did he actually mean when he wrote about the interweaving of worlds? She gathered her courage, however. Punctually at dusk, when the light drew out the shadows like long threads, Ola returned under the maple tree. There was a unique smell in the air - fresh earth, leaves and a hint of something hard to pinpoint, like pen ink. She sat down on the wall, clutching a letter and looking around. Suddenly, from within the tree, there came a quiet, melodious humming, impossible to attribute to any sound she knew. Everything in the courtyard froze. Ola felt the hair on her arms stand up on end. She moved closer to the trunk, when suddenly a light slipped out of a hollow in the bark - as if someone had switched on a lamp from inside....