His wife came into the pub a few seconds ago. His wife came in a few seconds ago. We have two points to consider: First, 'in' is an adverb when it does not head a noun phrase (which is the 'where it happens' that you mentioned, I suppose).
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Mister Micawber(which is the 'where it happens' that you mentioned, I suppose)Yes, your supposition is absolutely correct! (I'm sure you knew it)