Reclusive puzzle-setter, John ‘Ludwig’ Taylor (David Mitchell) sees his life of solitude turned upside down when his identical twin brother, James, disappears without a trace. In a quest to track James down, Ludwig assumes his brother’s identity, but by taking over every aspect of James’s life, Ludwig is forced to confront his own. Unlike Ludwig, James is no hermit; he's a family man and a highly respected DCI within Cambridge's busy Major Investigations Team.