In the middle of a very entertaining new song's finale (7)
I believe the answer is:
amongst
'in the middle of' is the definition.
(I've seen this before)
'a very entertaining new song's finale' is the wordplay.
'very' becomes 'most' (I've seen this in another clue).
'entertaining' is an insertion indicator (inviting in, as for dinner).
'new' becomes 'n' (abbreviation as in New Testament NT).
'finale' says to take the final letters.
The last letter of 'song' is 'g'.
'n'+'g'='ng'
'most' placed around 'ng' is 'mongst'.
'a'+'mongst'='AMONGST'
(Other definitions for amongst that I've seen before include "Surrounded by" , "Amid" , "In the midst of" , "Within the group of" , "Having been absorbed, perhaps" .)