Unthinking state of one in story chasing car (9)
I believe the answer is:
autopilot
'unthinking state' is the definition.
(as in doing something on autopilot)
'one in story chasing car' is the wordplay.
'one in story' becomes 'pilot' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'chasing' means one lot of letters go next to another (some letters chase after others).
'car' becomes 'auto' (synonyms).
'pilot' put after 'auto' is 'AUTOPILOT'.
'of' acts as a link.
(Other definitions for autopilot that I've seen before include "Action without self-awareness" , "requiring no help when stacking?" , "navigator" , "Device that keeps ships on a steady course" , "Robot flier?" .)