Eastern bloc writer Tania Roskov is driving to the border and the authorities pull her over. Commissar Gunzi is waiting and demands to see her papers. Tania presents them but Gunzi tells her that they’ve been waiting for her. She says that her papers are in order and she’s collecting an international prize for literature, but Gunzi says that it’s a disguised payment to encourage writers to slander their government. He puts her under arrest and tells her that her visa has been cancelled and they only issued it to determine if she would leave the country.
Peter and Diane are attending the prize ceremony so that Peter receives recognition for his work in invisibility. As they leave for the reception, Peter gets a call from Professor Kenig, the president of the prize committee, saying that he’s coming up. He tells Peter that Tania, their guest of honor, has been arrested at the frontier. The committee has decided to postpone the ceremony, but Peter suggests that they do more. He wants to slip past the border and rescue Tania.
Gunzi has Tania brought to him and accuses her of slandering the government. She insists that she has written nothing but the truth, but the general insists that she denounce her writing and the prize ceremony. When Tania refuses, Gunzi informs her that they will have “specialists” make her and has the guard take her away.
A western bloc general escorts Peter to the border and has his men cut through the tornado wire. Peter has a mine detector but the officer warns that it may not be enough. However, he tells Peter that they’ve picked that particular section of wire because he may be able to get help on the other side. There are woman laborers on the other side and one of them, Agasha, works for them. Peter grabs his pack and heads through the minefield. A sentry sees the mine detector hovering in mid-air and calls his superior, Captain Bera. The soldier reports seeing a floating stick and Bera takes some men to investigate. They realize that it’s a mine detector and open fire, and Peter drops the mine detector and blasts his way through the tornado wire with a grenade. While they examine it, Peter invisibly slips away.
Peter finds the labor gang and whispers to Agasha. She slips away and tells Peter that Tania has been taken to military headquarters. She points out a truck that is heading that way and goes back to the work crew, while Peter slips into the back of the truck before it drives away.
After a round of treatment, a soldier takes Tania out of her cell and brings her to Gunzi. He again suggests that she sign the statements, expressing his admiration for her talent. Tania points out that after what has happened to her, she’s surer than ever of the truth of what she’s written. Bera calls to tell Gunzi about what he saw and suggests that it was operated by remote control. Gunzi checks the prize ceremony invitation and confirms that Peter was going to receive a reward, and concludes that Peter crossed the minefield. He then sends out prison notices confirming Tania’s name and cell number.
Peter soon finds his way to military headquarters. Slipping by the guards, he goes to Tania’s cell and knocks out the sentry in front. However, Gunzi has left a pillow in place of Tania and closes the cell door behind Peter. He then has a soldier pump knockout gas into the cell, but Peter breaks the outside window for fresh air. Gunzi and his men don gas masks and enter the cell, and Peter fights his way past them and locks the cell door behind him. An upstairs guard hears Gunzi yelling and runs to investigate, and Gunzi sends him to get the master key.
Peter slips by him and looks for Tania in the other rooms, and finally locates her in Gunzi’s study. He breaks down the door and frees her, while below the guard frees Gunzi. Peter barricades the study door and takes Tania out the window, and then knocks out a driver and steals his truck. They drive out through the gate and Gunzi learns that they’re heading for the forest.
Peter drives to the frontier and has Tania hide in the trees. He then approaches Agasha and gets her attention. She finds Tania and warns her that the patrols are on alert and they have to get across the minefield. Agasha plans to get into one of the sentry tower, find the map showing the mines’ placement, and use a walkie-talkie to direct Peter and Tania through safely. Peter says that he’ll give the directions so that Agasha is safe and then make his way back on his own. Agasha agrees and returns to her work crew, and Peter takes Tania to the spot where he passed through the wire. A patrol is on duty and Peter knocks the two men out and takes their walkie-talkie.
Peter goes to the sentry tower and knocks out the soldier just as he spots Tania and prepares to shoot her. He then contacts Tania on the tower radio and directs her through the minefield. Bera overhears Peter on his walkie-talkie and tells Gunzi as he arrives. The commissar sends Bera and another soldier to kill Peter while he and the others go after Tania. They open fire and Tania takes cover, and Gunzi tells his men to fire at the mines. Peter kills one of Gunzi’s soldiers, drawing the others’ fire, and then continues giving directions to Tania. Gunzi realizes what they’re up to and shoots at Tania, and Peter shoots and wounds him. Bera and his man climb up the tower while Peter shoots Gunzi’s second man. Tania gets to safety while Peter trains a rifle on Bera and his man as they climb into the tower.
Later, Professor Kenig and Tania come to see Diane at the hotel. They ask if she has news of Peter, and Peter arrives and assures them that he was able to make it back by train. Kenig has Peter’s prize with him and Tania insists on giving it to Peter in person.