Blyton's vacuous designs (4)
I believe the answer is:
ends
'designs' is the definition.
(I've seen this before)
'blyton's vacuous' is the wordplay.
'blyton's' becomes 'Enid's' (Enid Blyton the author).
'vacuous' suggests removing the centre.
'enids' with its centre taken out is 'ENDS'.
(Other definitions for ends that I've seen before include "They may be made to meet!" , "Poles, aims" , "passes away" , "Brings to a close" , "Terminates, concludes" .)