Investigate how horrible dominating man disappeared (7)

I believe the answer is:

diginto

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'horrible dominating man disappeared' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'investigate how' is the wordplay.
'investigate' becomes 'dig' (I've seen this in another clue).
'how' becomes 'into' (I can't justify this - if you can you should believe this answer much more).
'dig'+'into'='DIGINTO'

Can you help me to learn more?

I've seen this clue in The Irish Times.

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