A voice inside the speaker keeps telling her to run: to leave everything behind, take a new name and a new personality, and wander with no destination. The poem is about the pull of reinvention, and about how much a person might want to escape who they have been. At first the voice is a whisper, but it grows louder each day until it fills her "heart and bones" like a drum shaking the floor.
What makes the mood so unsettling is that the voice is also tempting. It sings "with honeyed words," compared to moonlight slipping through a window, so it feels soft and beautiful rather than threatening. The speaker doesn't say whether she will obey it, which leaves her caught between longing and unease.
The ending is the sharpest moment. "Never be that girl again" suggests she is trying to get away from a past self, and the poem leaves us wondering whether that is freedom or a kind of erasing. The title, "Catch the Train," pushes toward leaving.