Long story in Shanghai regularly ignored (4)
I believe the answer is:
saga
'long story' is the definition.
(I've seen this before)
'shanghai regularly ignored' is the wordplay.
'regularly ignored' indicates alternate letters.
The alternate letters of 'shanghai' are 'SAGA'.
'in' acts as a link.
(Other definitions for saga that I've seen before include "Flag associated with a" , "Old story" , "Long heroic tale" , "Icelandic or Norse story" , "Heroic narrative" .)