When the devil drives, they must (5)
I believe the answer is:
needs
'when' is the definition.
Both the answer and definition are adverbs. Perhaps they are linked in a way I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for needs that I've seen before include "What we require" , "Requirements" , "Essentials" , "Is desperate for" , "Demands" .)