Steps adopted by coppers in epidemic (10)
I believe the answer is:
pestilence
'epidemic' is the definition.
(I've seen this before)
'steps adopted by coppers' is the wordplay.
'steps' becomes 'stile' (I've seen this in other clues).
'adopted by' is an insertion indicator (I've seen this in other clues).
'coppers' becomes 'pence' (I've seen this before).
'stile' placed inside 'pence' is 'PESTILENCE'.
'in' is the link.
(Other definitions for pestilence that I've seen before include "Epidemic disease with a high death rate" , "Fatal epidemic disease" , "it's an agent of evil" , "dire horseman?" , "that'll plague you" .)