Properly arranged (7)
'properly arranged' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for in order that I've seen before include "fitting" , "Able to operate" , "neat" , "Appropriate in the circumstances" , "organised?" .)
(Other definitions for orderly that I've seen before include "in a mess? No" , "Businesslike" , "Hospital attendant - neat" , "Officer's assistant" , "Hospital attendant; well behaved" .)