On the eve of the invasion of Normandy, a traitor on the base learns the location of one of the American landing sites, and Lieutenant Penny Bailey sees an officer leave the secrets office just before it explodes. Her CO asks her to strike up a relationship with the officer in order to gain evidence. But Penny finds herself attracted to this man and is dismayed to hear him speak in German on the phone. Should she have him arrested or listen to her heart? Before she can decide, a hidden factor brings it all to a head.