“I would never have believed it of any of you. Mr. Filch says you were up in the astronomy tower. It’s one o’clock in the morning. Explain yourselves.”
It was the first time Hermione had ever failed to answer a teacher’s
question. (Harry Potter and the Sorcerer’s Stone)
Is this a dummy-it construction or a cleft construction?
It is neither. “It” here has an implicit referent: the current situation. McGonagall asks a question, and instead of saying outright that Hermione did not answer, JKR invites the reader to “fill in the blank”.
In effect, the referent is the space between this and the preceding paragraph!
Source : Link , Question Author : Listenever , Answer Author : StoneyB on hiatus