I think most of you must have heard of the story of the pied piper. How about you attempt to retell the story? Perhaps a kid wants to save kitties (from someone or something) and lures them to safety, or maybe the child heard of the folk tale and wanted to do the same, but only managed to lure one cat (a neighbour’s cat or from someone who needed the cat; you can expand on that and create conflict).
Or the flute is magical and is the only way for the two of them to communicate. Perhaps the cat (or any other animal you choose) understands the child needs her and guides him to the flute.
You can go any way with this one, I think.