Vronsky enters the train car to look for his mother, but as he does so, a woman passes who causes him to do a double take: not so much because of her beauty, but because of her vivid features and the animation and passion flashing from underneath the surface. The woman also turns back to look at him.
Vronsky’s mother, the Countess Vronsky, introduces her to him. The woman is Anna Karenina, Oblonsky’s sister. The Countess tells Vronsky that the two women chatted about their sons for the entire train ride.
Almost immediately, Vronsky learns that the woman whom he has been captivated by is married and has a son.
As they all leave the station, a watchman is run over by a train. Anna is disturbed, viewing the death as a bad omen.
The death is, indeed, a bad omen: it foreshadows Anna’s own end.