What troubles diner over in Hellfire Club (5)
I believe the answer is:
ulcer
'what troubles diner' is the definition.
I can't tell whether this defines the answer.
'over in hellfire club' is the wordplay.
'over' shows that the letters should be reversed in order.
'in' indicates the answer is hidden within the clue.
'reclu' is hidden in the letters of 'hellfire club'.
'reclu' reversed gives 'ULCER'.
Can you help me to learn more?
(Other definitions for ulcer that I've seen before include "cause of suffering" , "Continuing source of pain" , "Cruel sort of body sore" , "Spot of bother" , "Cruel kind of body sore" .)