The Starlight Secret Society: An Atherton Manor Mystery

Three years ago, on a rainy afternoon, their mother told them about the Sunstone. They have not thought of it since. Not until the morning the line on the globe caught Clara's eye. Leo Atherton is eleven, Clara is ten, and Finn is eight. They have spent the past two years tiptoeing past their mother's closed door, eating breakfast with two empty chairs at the head of the table, and pretending they do not notice that their tutor has been giving them mornings off without saying why.
Then, on a quiet Tuesday in the family library, Clara sees a line on the old globe that should not be there. Finn, being Finn, spins the painted whirlpool. The globe opens. What the Atherton children find inside is a parchment, drawn long ago by an ancestor who did not want his secret found by accident. The map shows their own estate, in shapes that match the gnarl in the old oak and the curve of the south roof.
It mentions, in script smaller than a fingernail, something called the Sunstone. The story, their mother had told them, was that the stone did not give a person brilliance. It revealed the brilliance one already had, and could not yet see. The trail leads through their own neglected grounds. A conservatory that has not been opened in a generation. An aviary where the birds are not real. A ballroom of mirrors that lies.
A hedge labyrinth their disinherited great-aunt built one summer at a time. A grotto that listens. An observatory at the top of a wet hill in a storm. And four other children, Liam in his too-large tweed jacket, Beatrice with her notebook, Jasper with his compass, and small Lily with her bird-watching book, who have a copy of the same family lore. Liam's father has been waiting a long time for what the Athertons are about to find.
The Sunstone, the story said, can only do its work for someone who has earned the journey to find it. Whether Leo, Clara, and Finn, eventually no longer alone, can earn it before the wrong adults do; whether finding it will be enough to bring their mother back to the room she has not left in two years; whether what their family has been hiding for a hundred and twenty years is one stone or two: these are the questions the morning the globe opens has begun to ask.
For readers of Frances Hardinge's The Lie Tree, Trenton Lee Stewart's The Mysterious Benedict Society, and Jeanne Birdsall's The Penderwicks. A quiet literary middle-grade mystery for ages 9-13, with crossover appeal for adult readers of The Secret Garden and Piranesi.