Plan - an excellent idea? - to get behind beds (9)
I believe the answer is:
stratagem
'plan' is the definition.
(stratagem is a kind of plan)
'excellent idea? to get behind beds' is the wordplay.
'excellent idea?' becomes 'gem' (I can't explain this - if you can you should give a lot more credence to this answer).
'to get behind' says to put letters next to each other.
'beds' becomes 'strata' (I have seen 'hard beds' mean 'strata' so perhaps 'beds' could also mean 'strata').
'gem' after 'strata' is 'STRATAGEM'.
'an' is the link.
Can you help me to learn more?
(Other definitions for stratagem that I've seen before include "Devious ploy" , "Plan to deceive enemy" , "Artifice" , "Tag master with cunning plan" , "way to outwit opponent" .)