Why were the lights on in the Foster's home although it was very late?

The lights were burning in the Foster home because Winnie was missing.

Sometime later, the man in the yellow suit slipped down from the saddle and tied the Tucks' old horse to a bar of the Fosters' fence. He tried the gate. It was unlocked. He pushed through and strode up the path to the door of the cottage. Though it was very late now, almost midnight, the windows glowed golden: the family had not gone to bed. The man in the yellow suit took off his hat and smoothed his hair with long white fingers. Then he knocked at the door. It was opened at once by Winnie's grandmother, and before she could speak, the man said quickly, "Ah! Good evening! May I come in? I have happy news for you. I know where
they've taken the little girl."