Guys' partners crossing a river in foreign capital (7)
I believe the answer is:
dollars
'foreign capital' is the definition.
(US currency - capital can mean money)
'guys' partners crossing a river' is the wordplay.
'guys' partners' becomes 'dolls' (as in Guys and Dolls).
'crossing' means one lot of letters goes inside another (to cross can mean to go over or around).
'river' becomes 'r' (abbreviation).
'a'+'r'='ar'
'dolls' enclosing 'ar' is 'DOLLARS'.
'in' is the link.
(Other definitions for dollars that I've seen before include "US currency" , "ready for Americans" , "US money" , "Greenbacks" , "American currency" .)