Proceed to arrest (4)
I believe the answer is:
stem
I believe this clue is a double definition.
'proceed' is the first definition.
(thesaurus)
'arrest' is the second definition.
(both can mean to stop)
'to' acts as a link.
(Other definitions for stem that I've seen before include "Main stalk of a plant" , "Upward part of a plant" , "Stop the flow of, check" , "Restrain - staunch - supporter" , "Halt flow" .)