Where shoppers are going to happen (2,5)

I believe the answer is:

in store

I'm a little stuck... Click here to teach me more about this clue!

'going to happen' is the definition.
(thesaurus)

I don't understand the rest of the clue.

(Other definitions for in store that I've seen before include "To come" , "Approaching" , "Awaiting delivery" , "Soon to happen" , "Ready for future use" .)

I've seen this clue in The Daily Express.

Want a hint initially instead of a full solution? Install my app