Mark follows crazy leader to island (10)
I believe the answer is:
madagascar
'to island' is the definition.
(island nation)
'mark follows crazy leader' is the wordplay.
'mark' becomes 'scar' (mark left by an injury).
'follows' means one lot of letters go next to another.
'crazy' becomes 'mad' (synonyms).
'leader' becomes 'aga' (I've seen this before).
'mad'+'aga'='madaga'
'scar' after 'madaga' is 'MADAGASCAR'.
(Other definitions for madagascar that I've seen before include "foreign location" , "Land" , "Island republic in the Indian Ocean" , "Island nation" , "Island republic of Africa" .)