Armed criminal to come down to sleep (9)
I believe the answer is:
dreamland
'sleep' is the definition.
(I've seen this before)
'armed criminal to come' is the wordplay.
'criminal' is an anagram indicator.
'to' is a charade indicator (letters next to each other).
'come' becomes 'land' (landing is a kind of coming).
'armed' anagrammed gives 'dream'.
'dream'+'land'='DREAMLAND'
'down to' acts as a link.
(Other definitions for dreamland that I've seen before include "Sleep; ideal world" , "Utopia" , "Nod, perhaps" .)