Sam Coyle's father lived in the shadows - an undercover agent among the spies and radicals of Cold War London.

That world claimed his life, and Sam is haunted by his absence. He left nothing behind but his enemies; nothing to his daughter but his tradecraft and paranoia.

Now, her boyfriend Luke is missing too - the one person she could trust, vanished into the fog on the Kentish coast. To find him, Sam must follow uncertain leads into a labyrinth of blind channels and shifting ground. She must navigate the treacherous expanse of the salt marsh...