Task: Question Generation
Input (English):  A 1908 review of the book summarizes the light plot of the story in overenthusiastic fashion:
The story opens with a jump--literally. A young New Yorker, rich, of course, hears from his window on a night of fog and mist a woman's voice singing divinely. He falls in love with it head over heels and he falls downstairs in about the same way, he is such a hurry to see the singer. But by the time her reaches the street, lo! she has vanished, and only a policeman remains. Late on, this young, adventurous Mr. Hillard again meets the young, adventurous singer under most mystifying circumstances. They dine together, but she comes in mask. What the voice has begun, the masks puts the finishing touches to. From then on Hillard is full forty fathoms deep in love and curiosity. Then the scene shifts to Italy, with the shifting fortunes of an American comic opera company, stranded at Venice. The beautiful singer becomes the prima donna of this company. The soubrette is one Kitty Killigrew, and around her flourishes a most enticing, exciting and enlivening subplot. She dances her way straight into your heart. Amusing things happen at Venice. Thrilling things happen at Monte Carlo. At Florence the climax is reached, and it makes you fairly gasp with its intense interest. At Bellaggio, the loveliest of lovely spots in the land of love, the curtain goes down on happy lovers.
Output (English): What does Mr. Hillard hear when he opens the window?