Shanghai regularly deserted? It's a long story (4)
I believe the answer is:
saga
'a long story' is the definition.
(a saga is a long and complicated story)
'shanghai regularly deserted?' is the wordplay.
'regularly deserted?' means one should take alternating letters (letters removed at regular intervals).
The alternating letters of 'shanghai' are 'SAGA'.
'it's' is the link.
(Other definitions for saga that I've seen before include "A long adventurous story - it's a gas" , "Heroic narrative" , "Norse narrative" , "Epic story" , "Norse epic" .)