In the final sentence of the novel, a simile likens the disappearances at Hanging Rock to the well-known, real-world mystery of the Marie Celeste. Through this historical allusion, Lindsay underlines the unresolved nature of the mystery at the heart of her story—and in this way communicates the final impression she wishes to leave the reader with. 

Chapter 17, the novel's last chapter, takes the form of an article published in a Melbourne newspaper. Commemorating the 13th anniversary of the disappearances at Hanging Rock, the writer of the article likens the so-called "College Mystery" to the "celebrated case of the Marie Celeste":

Thus the College Mystery, like that of the celebrated case of the Marie Celeste, seems likely to remain forever unsolved.

The Marie Celeste was a merchant brigantine found abandoned in the Atlantic Ocean in 1872. Although the ship was in good condition when it was discovered, the captain and crew were gone. Since then, the mystery has remained unresolved, but it has resulted in many theories. Some of these resort to supernatural explanations.

It's significant that Lindsay chooses to end the novel with this allusion. By placing her story in a lineage with an unexplained and inexplicable mystery of the real world, she underscores the uncanny atmosphere that develops over the course of the novel.

Another thing worth noting is that the story ends with a different voice from that which narrates the first 16 chapters. Discussing the characters and events with a greater distance than the novel's predominant narrator, the writer of the fictional newspaper clipping sums up the story in a much briefer and more journalistic way than how it's been told up until this point. However, this secondary narrator corroborates the impression given by the former narrator: that the disappearances in the story, like those onboard the Marie Celeste, have no clear answer.