Turn over and turn key after writer (5)
I believe the answer is:
upend
'turn over' is the definition.
(I know that upend is a more specific form of the action the turn over)
'turn key after writer' is the wordplay.
'turn' becomes 'U' (a 'U-turn' is a kind of turn).
'key' becomes 'd' (musical key).
'after' says to put letters next to each other.
'writer' becomes 'pen' (something which writes).
'd' put after 'pen' is 'pend'.
'u'+'pend'='UPEND'
'and' is the link.
(Other definitions for upend that I've seen before include "Flip" , "Put into disarray" , "Turn top to bottom" , "Turn upside-down" , "Stand erect" .)