Dug into (6)
I believe the answer is:
probed
'dug into' is the definition.
('probe' can be a synonym of 'dig into')
This is the entire clue.
(Other definitions for probed that I've seen before include "Investigated closely as dentist does a tooth" , "Questioned or examined thoroughly and closely" , "Searched" , "Examined, dug into" , "Physically examined" .)