(idiomatic)Used to add emphasis to a question or statement.
What the devil are you doing here at this time of night?
1749, Henry Fielding, The History of Tom Jones, a Foundling
“Brother,” said she, “whatever message Mr Blifil thinks proper to send to my niece shall be delivered to her; and I suppose she will want no instructions to make a proper answer. I am convinced she will not refuse to see Mr Blifil at a proper time.”—“The devil she won’t!” answered the squire.