Most timid and quiet, indeed? Not in the end (6)
I believe the answer is:
shyest
'most timid' is the definition.
(I've seen this before)
'quiet indeed? not in the end' is the wordplay.
'quiet' becomes 'sh'.
'indeed?' becomes 'yes' (agreeing).
'in the end' indicates one should take the final letters.
The last letter of 'not' is 't'.
'sh'+'yes'+'t'='SHYEST'
'and' is the link.
(Other definitions for shyest that I've seen before include "Most retiring" , "Most reticent" , "Most timid" , "Most diffident" , "Most bashful or self-conscious" .)