Stream running into the river in exciting story (8)
I believe the answer is:
thriller
'exciting story' is the definition.
(I've seen this before)
'stream running into the river' is the wordplay.
'stream' becomes 'rill' (rill is a kind of stream).
'running into' means one lot of letters goes inside another.
'river' becomes 'r' (abbreviation for river).
'rill' put inside 'the' is 'thrille'.
'thrille'+'r'='THRILLER'
'in' is the link.
(Other definitions for thriller that I've seen before include "Exciting novel/film, etc" , "Exciting book/film" , "Michael Jackson album; novel" , "The Birds', say" , "best-selling album" .)