Screens from the East with crimson flowers outside (9)

'screens' is the definition.
(reredos is a kind of screen)

'the east with crimson flowers outside' is the wordplay.
'the east' becomes 'e' ('E' can be a synonym of 'east').
'with' means one lot of letters go next to another.
'crimson' becomes 'red' ('red' can be a synonym of 'crimson').
'flowers' becomes 'roses' (I've seen this before**).
'outside' means one lot of letters goes inside another.
'e'+'red'='ered'
'ered' put within 'roses' is 'REREDOSES'.

'from' is the link.