An anonymous letter arrives at the offices of the Clarendon English Dictionary containing a challenge for the team of lexicographers working there. It's clear that's it's not the usual run-of-the-mill, eccentric enquiry. The letter hints at secrets, lies and a year. 2010. For Martha Thornhill, the new senior editor, that year can mean only one the summer her brilliant, beautiful older sister Charlie went missing.
After a decade living abroad, Martha has returned to her father, her family home and the city whose institutions have defined her family, but the ghosts she thought at rest were only waiting for her to return.
More letters arrive, pointing towards a secret in the heart of the dictionary itself. As Martha and her colleagues start pulling apart the clues, the questions become more insistent and troubling. Charlie's disappearance is one of a series of secret absences going back centuries, and someone wants to keep those secrets buried.