Dog's last to find out about bitch (7)
I believe the answer is:
grumble
'bitch' is the definition.
(I've seen this before)
'dog's last to find out' is the wordplay.
'last' indicates one should take the final letters.
'to find out' becomes 'rumble' ('rumble' can mean to discover a scheme).
The last letter of 'dog' is 'g'.
'g'+'rumble'='GRUMBLE'
'about' acts as a link.
(Other definitions for grumble that I've seen before include "Complain, protest" , "Moan" , "what Meldrew does" , "Complain, be a grouch" , "Express dissatisfaction" .)