In the aftermath of Seamus stepping off the train into the icy river below, Anna screams into the rushing cold air, both mourning him and hating him. She recalls the helpless image of Seamus’s body flailing and striking the water before the train carried her past the bridge and the river faded from view.

The screaming becomes a release for Anna, unleashing long-suppressed pain from the past twelve years. When the scream finally drains from her, she remembers Seamus’s last instruction: "You know what to do. You can end this." At the time, she had been too overwhelmed by betrayal and despair to understand.

Anna considers that Seamus forced a gun into her hand, and she first assumes he wanted her to finish his plan by killing Jack Lapsford and claiming vengeance. But she replays another of his statements: "When I got the opportunity to murder one of those bastards, I took it." One word—"one"—stands out to her.

Anna shuts the open doors and collapses beside them, throat raw from screaming. As she gulps air and weeps, she scrutinizes Seamus’s admissions. Of all the killings on the train, Seamus only confessed to one: Judd’s murder. He never took credit for Edith’s smothering, Herb’s throat-slitting, or Sal’s shooting.

From this, Anna infers a crucial truth: the other murders must have been committed by someone else. With Seamus gone, the threat remains. Anna resolves that there is another killer aboard and that she must now act to end the violence.