River featuring in popular novel (4)
I believe the answer is:
arno
'river' is the definition.
(I've seen this before)
'in popular novel' is the wordplay.
'in' indicates a hidden word.
'ARNO' is hidden in the letters of 'popular novel'.
'featuring' acts as a link.
(Other definitions for arno that I've seen before include "European river" , "Florence's river" , "River of 4 down?" , "Pisa's river" , "Banker" .)