On Valentine's Day in 1900, an enigmatic headmistress allows her pupils to picnic at Hanging Rock. There, in the strange brooding landscape, something unthinkable happens.

Hester's three star pupils and a governess have disappeared. Led by a dogged Sergeant, local men search for the missing. Has something supernatural befallen them? Or has a human outrage occurred? An aristocratic young Englishman, Michael Fitzhubert, was the last person to see the girls, and when the search is abandoned, he is compelled to return to the Rock where he makes a shocking discovery.

The missing Rothschild heiress, Irma Leopold, has been found, remarkably unharmed, but claiming to remember nothing. Meanwhile, rumors spread and the Sergeant turns his attention to the College. What secrets lie hidden behind the locked gates? His investigation intensifies Hester's paranoia and she grows certain that the young orphan, Sara, knows something about the disappearance.

Hester struggles to contain mounting hysteria as aftershocks from the disappearance continue to disrupt the old order. A mysterious visitor summons memories of Hester's dark past, whilst Sara seeks escape from the college. Meanwhile, we are taken into the story of the missing girls in the months leading up to the picnic, and the dark stain of the unsolved mystery continues to spread.

French governess, Mademoiselle, is growing increasingly suspicious of Mrs Appleyard's erratic behavior, and fears the worst when she is told that Sara was unexpectedly collected by her guardian, unseen by any other staff. As Mademoiselle searches for answers, the Sergeant travels to Melbourne to seek a last interview with Irma, and a secret vow made by the missing girls is revealed.

Hester has grown increasingly certain that her vengeful husband's behind the disappearances and is coming after her. As she prepares to flee, the arrival of Sara's guardian provides conclusive proof of Mrs Appleyard's lies. As Hester travels to the Hanging Rock, we finally learn all that led to her demise. The haunted past she ran from, and the secret lives of the missing college girls.