Click for larger image

After the United States Office of Strategic Services learns that Germany is receiving large shipments of pitchblende, material that is needed for the development of nuclear power, Colonel Walsh recruits his old friend, nuclear physicist Alvah Jesper, to work with the O.S.S.  Alvah is asked to travel to Switzerland, where he will contact Austrian scientist Dr. Katerin Loder, who has escaped from Germany, and discover what she knows about Germany's efforts to build an atomic bomb.

Using the name Andrew Wilson, Alvah meets with Katerin at a hospital.  When she discloses that the Germans have threatened to kill several anti-Nazis every day that she remains in Switzerland, Alvah suggests that she return to Germany and spy for the Americans.  Before arrangements can be made, however, Katerin is kidnapped.  In order to get her back, Alvah frames a German operative named Ann Dawson, who is staying at his hotel, and forces her to reveal where Katerin has been taken.

After Katerin is killed during the subsequent rescue attempt, Alvah proposes that he try to contact Giovanni Polda, the Italian scientist with whom Katerin was working.  Alvah is smuggled into Italy by several members of the underground, including Pinkie, Marsoli and an attractive woman named Gina.

Posing as a German scientist, Alvah contacts Polda, who explains that although he would like to help Alvah, the fascists are holding his daughter Maria hostage.  Alvah then offers to get both Maria and Polda out of the country.  While Alvah waits for the Italians to rescue Maria, he hides out at Gina's.  After Alvah is seen in her room, however, he and Gina are forced to move several times.  Soon, the two of them fall in love.

When they are notified that Maria is safe, they set out to bring Polda to the rendezvous.  During the pick up, Alvah is forced to kill the security guard who has been assigned to Polda.  After a long drive, Gina, Alvah and Polda arrive at the rendezvous, where Polda reveals that the woman claiming to be Maria is not his daughter.  From the woman, Polda learns that Maria died six months earlier, and that now the fascists, who have followed her to the hideout, have surrounded the house.

During the ensuing gunfight, Pinkie orders Gina to take Alvah and Polda out through the cellar while the others stay behind to draw the soldiers' fire.  Supporting the ailing Polda between them, Alvah and Gina make their way across the fields to the waiting airplane.  Alvah asks Gina to come with them, but she refuses, believing that her work in the Italian resistance is too important.  Alvah then promises to return for her after the war is over.