Concoct, as a plan (5)
I believe the answer is:
hatch
'concoct as a plan' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hatch that I've seen before include "Opening with removable door" , "contrive to > emerge in > shade" , "Breed" , "serve here?" , "Draw fine lines" .)