The most common and most likely answer to this crossword clue is the 4 plus 4 plus 7 letter word WHAT LIES BENEATH
W
H
A
T
L
I
E
S
B
E
N
E
A
T
H
Buddy explains!
The straight part
We know that "Film" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case film = what lies beneath.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.