Lark struggles to settle when her Roma family moves to a new site on the coast.

Her mother is ill, her little sister Snow has stopped speaking and she has fallen out with her best friend.

Who is following her in the fog? Does she keep seeing a strange girl in a green dress, or is her sister playing tricks on her?

When a local woman tells her 'the girl' comes to take sisters, Lark knows only she can save her family.