It's not often you get a "war mystery" film, and of course when you do, you are usually dealing with spies.
In this case, the mystery is about a German spy dressed up as an American soldier during World War II. He has forged papers, and his goal is to make it to a town where a resistance member is kept. This resistance member is a liaison between all the groups, and obviously knows connections to each. He would be a great prize.
We see the command given to the spy, but not his face, and we are then taken to a site where American soldiers have been whittled away from their individual units, and eight join up, including the by the book lieutenant and the veteran sergeant.
This is a top mystery and a top war film. It combines both elements, and it's difficult to say why without spoilers. Suffice to say that the characters are very believable, the action very credible, and the spy is exactly the type of person who would be seen as most successful.
There is incredible eye candy with a couple of Italian women, one of which is guaranteed to make any young man fall in love/lust. This woman wears boots and possibly inspired the Nancy Sinatra song.
The title lets you know that when they are whittled down to four, they will find the spy (or he will succeed and exit). I don't think it's a spoiler to say that the ones who die before this are given high drama to their deaths, although the first is a wounded man who never lasts long enough for the high drama. With each casualty, our director succeeds in making you feel more and more empathy for them. The last American who dies is given the most tragedy, as we see him to be the possible hero.
This is a lost gem, and easily the best of the war mysteries. Tons better than the blockbuster big budget bits of propaganda that are more famous.