Contemporaries of Duke, say, scramble to protect Harry’s heart (4,5)
I believe the answer is:
peer group
'contemporaries' is the definition.
(I've seen this before)
'duke say scramble to protect harry's heart' is the wordplay.
'duke say' becomes 'peer' (duke is a kind of peer).
'scramble' becomes 'go up' (to scramble is to climb or go up).
'to protect' means one lot of letters goes inside another (inserted letters are protected or taken in).
'heart' means to look at the middle letters.
The centre of 'harry' is 'r'.
'goup' going around 'r' is 'group'.
'peer'+'group'='PEER GROUP'
'of' is the link.
(Other definitions for peer group that I've seen before include "set to meet in the upper house?" , "Those of equal age and ability, often influential" , "contemporaries - with 15d" , "People who are associated with and of equal status" , "A segment of society who are associated and of equal status" .)