Mexican drink in story — the hard stuff? (9)
I believe the answer is:
limescale
'hard stuff?' is the definition.
(hard substance)
'mexican drink in story' is the wordplay.
'mexican drink' becomes 'mescal' (Mexican alcoholic drink).
'in' is an insertion indicator.
'story' becomes 'lie' (story can mean a fabrication).
'mescal' put inside 'lie' is 'LIMESCALE'.
'the' is the link.
(Other definitions for limescale that I've seen before include "Flaky deposit in kettle" , "flaky stuff" , "in the water that's the hard part" , "It builds up on pipes and kettles" , "Kettle's encrustation" .)