Two men escape the prison of Devil's Island. One is Paul Lavond, a former banker wrongly imprisoned for murder and swindling; the other is a mad scientist named Marcel. After weeks of escape, they join a small house busy by Malita, Marcel's crippled wife.
She continued the experiences of her husband during his captivity. In a goal purely humanitarian, the two have invented a process to reduce considerably the size of human beings and the impressive quantity of mini dogs is there to testify their success. Unfortunately the shrinking process damages the brain of the victims and although they can no longer act by themselves, it is still possible to control them by the thought of others persons. This evening, Lavond is woken by noises downstairs. He enters Marcel's laboratory and discovers that they come to reduce Lachna, their servant. But Marcel dies of a heart attack. Distraught by the death of her husband, Malita implores Lavond to stay and to continue with her the work of the scientist. However, he has another plan to the mind.
He decides to use the invention of the scientist to appease his revenge thirst towards Coulvet, Radin and Matin, the three Parisian bankers associates that have schemed his condemnation and arrest. Frightened by the escape of Lavond that they know on the point to return to revenge, they propose a reward of 50.000 Francs for the one who will stop the convict. The police researches are vain. Lavond has changed identity. He is now Madame Mandelip, a little old woman, a dollmaker in a shop in the Parisian backstreets.
Thus disguised, Lavond visits Radin and makes him the demonstration; a miniature horse. Concerned Radin visits the shop of the old woman where he discovers the tremendous doll Lachna. Lavond shows Radin the small stiletto of the doll and stabs him with. The knife is in fact covered by a product that paralyzes its victims. Thus trapped, Radin will be the first to fall under the instrument revenge of the ex-banker.
Lavond decides to visit his daughter, Lorraine, who works vigorously in a laundry. Although in love with Toto, a cab driver, Lorraine does not resign to the marriage, disturbed by the disgrace of her father and the suicide of her mother. But before to unveil his identity to his daughter, Lavond starts the next phase of his revenge. He visits Madame Coulvet and sells her a doll, Lachna. That night Lavond programs Lachna to steal the jewels of the banker and to knock to his tour the vilain. It is now Matin who receives a letter. If he does not confess his crimes and the innocence of Lavond he will become his next victim this evening at 10 o'clock...
Spoiler ! the end of the story is revealed below…
Taken by panic Matin asks the protection of the police. But while 10 approach, Matin can no longer wait and avoids his horrible fate. He confesses and innocent Lavond. For this last, justice is made, even if he cannot retreive the life he had before. He decides to destroy the equipment of the madman, finding the idea inhuman and frightful. But Malita wants to continue at any costs Marcel's work and ahead his refusal, she programs the doll Radin on him but she makes explode the shop. In the Toto's Taxi, Lavond unveils his identity to the young man. On the Eiffel Tower, Paul meets Lorraine and makes him pass for a friend of her father who carries her a message. Paul Lavond brings the necessary moral repair for his daughter that will now be able to live happy.