In a serious way, shelter in the heart of ancient (9)
I believe the answer is:
earnestly
'in a serious way' is the definition.
(I know this)
'shelter in the heart of ancient' is the wordplay.
I cannot quite understand how this works, but
'shelter' could be 'nest' (I've seen this in other clues) and 'nest' is present in the answer.
'ancient' could be 'early' (I've seen this in another clue) and 'early' is located in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for earnestly that I've seen before include "Zealously" , "Showing commitment" , "with heart and soul" , "Showing serious intent" , "In all seriousness" .)