Misdeed on a European peninsula (6)
I believe the answer is:
crimea
'european peninsula' is the definition.
(I've seen this before)
'misdeed on a' is the wordplay.
'misdeed' becomes 'crime' (I've seen this before).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'crime'+'a'='CRIMEA'
(Other definitions for crimea that I've seen before include "former war site" , "Ukrainian peninsula, theatre of 1853-6 war" , "historic war zone" , "High-quality black tea" , "Black Sea region" .)