He's in a spy novel going on pointlessly (9)
I believe the answer is:
sisyphean
'going on pointlessly' is the definition.
(as in a pointless or Sisyphean task)
'he's in a spy novel' is the wordplay.
'novel' indicates an anagram.
'hes'+'in'+'a'+'spy'='hesinaspy'
'hesinaspy' anagrammed gives 'SISYPHEAN'.
(Other definitions for sisyphean that I've seen before include "requiring unending effort" , "such an arduous task" , "Denoting an unfinishable task" , "Endlessly laborious" , "uphill" .)