When an anonymous letter is delivered to the Clarendon English Dictionary, it puzzles the team of lexicographers working there. It soon becomes clear that this is not the usual eccentric enquiry. The letter hints at secrets, lies, and a particular year. For Martha Thornhill, the new Senior Editor, the date can mean only one thing: the summer her brilliant, beautiful older sister Charlie went missing. After a decade spent living abroad, Martha has returned to her father, her home, and the city whose institutions have defined her family. But the ghosts she had thought to be at rest seem to have been waiting for her to return. When more letters arrive and the team pull apart the clues within them, the questions become more insistent and troubling.