Play, Pinter's first – English gentry involved (4,4)
I believe the answer is:
peer gynt
'play' is the definition.
(I've seen this before)
'pinter's first english gentry involved' is the wordplay.
'pinter's first' becomes 'p' (1st letter of 'pinter').
'english' becomes 'e' (abbreviation).
'involved' indicates an anagram (involved can mean confusing or complex).
'gentry' anagrammed gives 'ergynt'.
'p'+'e'+'ergynt'='PEER GYNT'
(Other definitions for peer gynt that I've seen before include "Norse legend" , "Solveig loved him (Ibsen)" , "Ibsen drama" , "(Son of Ase in) Ibsen play" , "Ibsen play (for which Grieg wrote music)" .)