Mad character to demonstrate locks, we hear (5,4)
I believe the answer is:
march hare
'mad character' is the definition.
The definition suggests a singular noun which matches the answer.
'demonstrate locks we hear' is the wordplay.
'demonstrate' becomes 'march' (synonyms).
'locks' becomes 'hair' (locks can mean hair).
'we hear' indicates a 'sounds like' (homophone) clue.
'hair' sounds like 'hare'.
'march'+'hare'='MARCH HARE'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for march hare that I've seen before include "character encountered by Alice" , "One in Tea Party" , "Animal in state of wild behaviour, starting with 3rd month?" , "Proverbially mad creature" , "seen at endless party" .)