Intense pain (5)
'intense pain' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for agony that I've seen before include "Suffering - anguish" , "woe" , "Torture" , "Distress" , "Severe pain, mental or physical" .)
(Other definitions for throe that I've seen before include "pain" , "Other (anag.)" , "Convulsion" , "Spasm - pang" .)