Tired secret agent takes refuge (6)
I believe the answer is:
sleepy
'tired' is the definition.
(I've seen this before)
'secret agent takes refuge' is the wordplay.
'secret agent' becomes 'spy' (spy is a kind of secret agent).
'takes' indicates putting letters inside.
'refuge' becomes 'lee' (I can't justify this - if you can you should give a lot more credence to this answer).
'spy' enclosing 'lee' is 'SLEEPY'.
Can you help me to learn more?
(Other definitions for sleepy that I've seen before include "Ready to nod off" , "needing a rest" , "One of the Seven Dwarfs" , "over-tired" , "Dozy" .)