Various folk plunging into the depths with energy (7)
I believe the answer is:
diverse
'various' is the definition.
(I know that various can be written as diverse)
'folk plunging into the depths with energy' is the wordplay.
'folk plunging into the depths' becomes 'divers' (deep-sea divers).
'with' means one lot of letters go next to another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'divers'+'e'='DIVERSE'
(Other definitions for diverse that I've seen before include "Widely varied" , "Different and various" , "Miscellaneous" , "I served in many ways" , "Differing" .)