Door's opening, better frantically peer in here? (7)
I believe the answer is:
debrett
'peer in here?' is the definition.
(Debrett's Peerage is a guide to the UK peerage)
'door's opening better frantically' is the wordplay.
'opening' indicates taking the first letters.
'frantically' indicates an anagram.
The initial letter of 'doors' is 'd'.
'better' with letters rearranged gives 'ebrett'.
'd'+'ebrett'='DEBRETT'
(Other definitions for debrett that I've seen before include "Man giving name to publishers best known for books on etiquette" , "List of the British aristocracy" , "Founder of book on the peerage" , "Peerage reference book" , "Peerage guide" .)