Errand boy approaching artist's captivating work (4,6)
I believe the answer is:
page turner
'captivating work' is the definition.
(I've seen this before)
'errand boy approaching artist's' is the wordplay.
'errand boy' becomes 'page' (page is a kind of errand boy).
'approaching' is a charade indicator (letters next to each other).
'artist' becomes 'turner' (painter JMW Turner).
'page'+'turner'='PAGE-TURNER'
(Other definitions for page turner that I've seen before include "exciting work" , "Pianist's assistant" , "Enthralling work" , "compelling work" , "exciting novel?" .)