A grim tortuous character performance (9)
I believe the answer is:
rigmarole
'performance' is the definition.
(I've seen this before)
'a grim tortuous character' is the wordplay.
'tortuous' is an anagram indicator.
'character' becomes 'role' (synonyms).
'a'+'grim'='agrim'
'agrim' is an anagram of 'rigma'.
'rigma'+'role'='RIGMAROLE'
(Other definitions for rigmarole that I've seen before include "Complex procedure" , "Lengthy and complicated procedure" , "boring series" , "A grim role for long rambling statement" , "garbled nonsense" .)