A la sombra del puente

In Mexico City, two crooks, Tigre and Chebo, botch a train robbery and kill the engineer, then confess their misdeed to their associate, Braulio Nájera, who is waiting nearby. Antonio Ceballos, leader of a nascent, secret railroad union, finds the body and is arrested by the railroad police as the murderer. Accused at his trial of being an anarchist, Antonio forbids his associates to speak in his defense and is found guilty. Antonio proclaims his innocence and warns Judge Salazar that his verdict will return to haunt him, but Salazar imposes the maximum sentence of twenty years imprisonment. Tigre, fearful of being identified by Antonio as the real killer, has Antonio killed in prison. Ten years later, after the union has become a reality and a social force, Antonio's son, Antonio, Jr., runs for office in the legislature and begins to gather evidence to exonerate his father. Meanwhile, Tigre, having been imprisoned for another crime, is released due to a tubercular condition and is met by his henchmen Chebo and Cherifas. Worried that Antonio's public campaign to exonerate his father could cause his return to prison, Tigre decides to eliminate him. One evening, while Rosaura, Braulio's sister, is talking with a carousel operator near the bridge under which she lives, Judge Salazar, who has become mentally unstable, approaches them in a confused daze, then wanders away. Upset when he learns of Antonio's mission and after being threatened by Tigre and Chebo, Braulio confesses to his father Pedro that he knew of the engineer's murder years before and was too frightened to speak at the trial. Later that evening, while following a lead to locate Braulio, Antonio encounters Rosaura and although neither knows the other's surname, they fall in love. When it begins to rain, Rosaura invites Antonio to her home. The couple run into the confused Judge and take him with them. Once there, however, Rosaura discovers Antonio's full identity and asks him to leave, fearful he will discover Braulio's connection with the past. Shortly afterward, Antonio learns Braulio is Rosaura's brother and returns to the Nájeras' home to confront Braulio and Pedro, and demand that they clear his father's name. When Pedro tells Antonio that his father was an innocent martyr, Antonio becomes even more determined to find his father's killer. Meanwhile, Tigre learns Antonio is at the Nájera home, but Chebo refuses to take part in his plot to murder Antonio. Tigre then orders Cherifas to kill Chebo. After being shot twice, Chebo falls from a bridge onto a passing train. Later, Salazar agrees to help clear Antonio's father, but Antonio insists the only way is to locate the real murderer. Tigre then walks into the house and directs Braulio to get rid of the judge, but the younger man balks. Suddenly Chebo stumbles in, covered in blood and dirt, and demands that Tigre confess his part in the engineer's murder, then collapses and dies. While Braulio hides the body in a back room, Antonio declares that Chebo's appearance confirms Tigre and Braulio's collusion in his father's death. Pedro assures Antonio he will testify about the engineer's murder and reminds Antonio his father never sought revenge. Frightened for Braulio, Rosaura urges Antonio to take no action. Just then two policemen searching for Salazar arrive and Antonio tells them that Tigre has just murdered Chebo. When they search for his body, however, it has mysteriously vanished. Still anxious for Braulio, Rosaura pleads with Antonio to admit that Chebo's appearance was merely a dream. Disappointed by her request, Antonio nevertheless retracts his accusation. Advised by the departing policemen to leave, Tigre goes outside and gathers his henchmen, telling them to split up and shoot when Tigre signals them by lighting a match. Having seen Tigre make his plans through the window, Rosaura warns Antonio not to go outside. Disgusted with her fear and his own hesitation, Antonio rushes outside, but Tigre's men, unable to see clearly through the rain, shoot and miss him. Rosaura dashes to Antonio's side and is soon followed by Braulio wielding a pistol, determined to prove his courage at last. He advances on Tigre and his men, but at Tigre's signal is shot down. Knowing they are trapped, Rosaura prays for their salvation and in moments the carousel goes on, attracting the attention of the neighborhood police. When the carousel operator leads them to Rosaura and Antonio, Tigre can only watch helplessly as the police escort the couple away. As Tigre leaves his post, a vagabond, seeing the remains of a cigarette butt, retrieves it and lights up. Mistaking that for the signal, Tigre's henchman shoots and kills Tigre.