Gaunt young Irene performs in musical (5,3,4,3)
I believe the answer is:
annie get your gun
'musical' is the definition.
(annie get your gun is a musical)
'gaunt young irene performs' is the wordplay.
'performs' indicates an anagram.
'gaunt'+'young'+'irene'='gauntyoungirene'
'gauntyoungirene' anagrammed gives 'ANNIE GET YOUR GUN'.
'in' is the link.
(Other definitions for annie get your gun that I've seen before include "film" , "Girl instructed to defend her own" , "musical" , "call to arms" .)