Risk hiding in the plain curtains (5)
I believe the answer is:
incur
'risk' is the definition.
(I've seen this before)
'hiding in the plain curtains' is the wordplay.
'hiding' indicates the answer is hidden within the clue.
'INCUR' is hidden within 'in plain curtains'.
(Other definitions for incur that I've seen before include "Invite, bring about" , "Become subject to (something unwelcome)" , "Become responsible for" , "Arouse" , "Sustain" .)