Where you'll find the van in action (5,4)
I believe the answer is:
front line
'where you'll' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'the van in action' is the wordplay.
'the van' becomes 'front' (van can mean the front part of something).
'in action' becomes 'line' (I can't explain this - if you can you should give a lot more credence to this answer).
'front'+'line'='FRONT LINE'
'find' acts as a link.
Can you help me to learn more?
(Other definitions for front line that I've seen before include "Where the fighting takes place" , "sharp end" , "Most advanced troops" .)