Words are important to Gretel, always have been. As a child, she lived on a canal boat with her mother, and together they invented a language that was just their own. She hasn't seen her mother since the age of sixteen, though - almost a lifetime ago - and those memories have faded. Now she works as a lexicographer, updating dictionary entries, which suits her solitary nature. A phone call from the hospital interrupts Gretel's isolation and throws up questions from long ago. She begins to remember the private vocabulary of her childhood. She remembers other things, too: the wild years spent on the river; the strange, lonely boy who came to stay on the boat one winter; and the creature in the water - a canal thief? - swimming upstream, getting ever closer. In the end there will be nothing for Gretel to do but go back.