Friend taking in key performance (7)
I believe the answer is:
matinee
'performance' is the definition.
(I know that matinee is a type of histrionics)
'friend taking in key' is the wordplay.
'friend' becomes 'mate' (mate is a kind of friend).
'taking' means one lot of letters goes inside another.
'key' becomes 'E' (musical key).
'mate' going around 'in' is 'matine'.
'matine'+'e'='MATINEE'
(Other definitions for matinee that I've seen before include "sort of jacket" , "Afternoon performance (of play etc)" , "After lunch, show" , "Afternoon showing of play" , "First jackets" .)