They might solve dastardly con from this? (3,8,4)
I believe the answer is:
new scotland yard
'this?' is the definition.
The definition suggests a singular noun which matches the answer.
'they might solve dastardly con' is the wordplay.
'they might' becomes 'new' (I can't justify this - if you can you should give a lot more credence to this answer).
'solve' indicates anagramming the letters (I've seen 'solved' mean this (the anagram must be solved)).
'dastardly'+'con'='dastardlycon'
'dastardlycon' is an anagram of 'scotlandyard'.
'new'+'scotlandyard'='NEW SCOTLAND YARD'
'from' acts as a link.
Can you help me to learn more?
(Other definitions for new scotland yard that I've seen before include "A place for pigs!" , "police HQ" .)