Old misery comes in to play (7)
I believe the answer is:
othello
'play' is the definition.
(play by William Shakespeare)
'old misery comes in to' is the wordplay.
'old' becomes 'o' (abbreviation).
'misery' becomes 'he'll' (I've seen this in another clue).
'comes in' means one lot of letters goes inside another.
'hell' inserted into 'to' is 'thello'.
'o'+'thello'='OTHELLO'
(Other definitions for othello that I've seen before include "Literary character" , "Shakespeare tragedy" , "board game" , "Hello to Shakespeare's Moor" , "Shakespearean role" .)