Mate is carrying round broken chain with a bad purpose (9)
I believe the answer is:
machinate
'bad purpose' is the definition.
The definition suggests a verb in its base form which matches the answer.
'mate is carrying round broken chain with a' is the wordplay.
'is carrying' indicates putting letters inside.
'round broken chain' becomes 'chin' (I can't justify this - if you can you should believe this answer much more).
'with' means one lot of letters go next to another.
'chin'+'a'='china'
'mate' going around 'china' is 'MACHINATE'.
Can you help me to learn more?
(Other definitions for machinate that I've seen before include "scheme" , "Plan" , "concoct a plot" , "Plot to do harm" .)