What the "in" diners at the restaurant had? (6)
I believe the answer is:
entree
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for entree that I've seen before include "Right to take part" , "Right of access; course" , "The right to go in to the dish" , "No way-out" , "Dish allowing one to go in?" .)