The troubling conceit of the plot has the hero take the villain’s face & voice. The FBI people who persuade Archer science can do this are killed along with the doctor; they may have misunderstood their doings. They had naively reassured Archer that it was all reversible. Castor takes a hint & returns the favor. Castor was in a coma, not dead… Now, each sees himself in the other; each sees the other in himself. Archer has to escape prison, while Castor has to lead the FBI. Each has to live with the other’s family.
Castor is strangely tempted by this new life. He complains of bourgeois family life, but shows little revulsion or incomprehension. Public life attracts him less; he has no notion of duty; whereas private life presents manifold attractions, else he might not break the law. His opinions about wife & daughter are distinctly old-fashioned; they turn on self-protection or self-reliance & private pleasures.
Castor is also quite apt to lead the police; perhaps the successful criminal’s craft is also the successful detective’s. But Castor is impatient; he has an ugly habit of killing his minions. As policeman, he destroys many criminals, receives the accolades of the country, & seems quite proud of his achievements. Strangely, he undoes much of the evil he has done. Apparently, being loved by the people might supplant his deviant erotic inclinations, could he abide by the laws… Formal rules cannot allow for his genius, but he envies Archer, whose journals he reads.
Archer is very different. When he sees his new face, hatred & pain disfigure his face. Before the final gunfight, Castor reproaches him for taking everything so personally. He says he murdered the boy by accident. Archer knows different. How could he allow the unjust man to thrive? Now he impersonates Castor, whom he had studied for years. He recoils at doing evil. The unthinkable is thinkable for him, or how catch Castor? But doable? Archer always chafed under the restraints that help criminals. The laws are a hard yoke to bear for him, too.
Archer finds no pleasure in killing policemen or helping criminals, but survival requires it. Perhaps the pleasures of crime conceal ugly necessity. We are shown something unusual about morality: Archer is such a hero that he spontaneously arouses shame & sacrifice in people, including criminals. He embodies everything they believe about morality. His shroud of death suggests he is a tragic hero.
The wife cannot tell which of the two is her husband until she tests the blood scientifically. Neither can the laws. Apparently, the administration even of justice is quite helpless to distinguish good men from bad. Only God knows men’s hearts truly.