When you meet up with the French rebels you will have a choice to go left to 
the Flak 88s or go through the house to the right. Go left to the guns. Kill 
all the Nazis around the gun and in the ditch leading to the next gun. Then, 
blow up the 88 and move on to the rest of the guns. After you blow up all the 
guns you will reach the house that you would have had to take if you went 
right. When you go in the house you must defeat a Nazi that is standing there 
waiting for you. Kill all the enemies in the house and fall through the burning 
floor. You will see you allies there waiting for you.