Tempestuous tale captivating millions (6)
I believe the answer is:
stormy
'tempestuous' is the definition.
('stormy' can be similar in meaning to 'tempestuous')
'tale captivating millions' is the wordplay.
'tale' becomes 'story' ('story' can be a synonym of 'tale').
'captivating' indicates putting letters inside (I've seen this in other clues).
'millions' becomes 'm' (abbreviation).
'story' enclosing 'm' is 'STORMY'.
(Other definitions for stormy that I've seen before include "Passionate" , "Full of violent outbursts" , "''... Weather''(song)" , "Wet and windy" , "Emotional" .)