what (in) the devil

An exclamation used to emphasize surprise, shock, or bafflement. Just what the devil is going on here? What in the devil? I just put my sandwich down, and now it's gone!

what in the devil

Used to ask a question about the nature of something or some activity while emphasizing one's surprise, frustration, irritation, etc. What in the devil is going on in here? I leave the room for two minutes, and you two start screaming like wild animals! A: "Dr. Murakami, come have a look at this strange egg we discovered." B: "What in the devil? I've never seen anything like this before in my life!" Ew, what in the devil is that horrible smell?