Pack turning towards vermin (5)
I believe the answer is:
tarot
'pack' is the definition.
(type of card pack)
'turning towards vermin' is the wordplay.
'turning' shows that the letters should be reversed in order.
'towards' becomes 'at'.
'vermin' becomes 'rot' (I am not sure about this - if you are sure you should believe this answer much more).
'at' back-to-front is 'ta'.
'ta'+'rot'='TAROT'
Can you help me to learn more?
(Other definitions for tarot that I've seen before include "Special cards for fortune-telling" , "One in special suit" , "Arcana cards" , "These cards are used by fortune tellers" , "These cards are used to tell fortunes" .)