Very quick train's ending in northern city (7)
I believe the answer is:
preston
'northern city' is the definition.
(city in the north of England)
'very quick train's ending' is the wordplay.
'very quick' becomes 'presto'.
'ending' indicates one should take the final letters (the ending of the word).
The last letter of 'train' is 'n'.
'presto'+'n'='PRESTON'
'in' is the link.
(Other definitions for preston that I've seen before include "City in Lancashire" , "Town in Lancashire" , "Administrative centre of Lancashire" , "English city" , "town in northern England" .)