When John ‘Ludwig’ Taylor’s (David Mitchell, Peep Show) identical twin, James, disappears off the face of the earth, John takes over his brother’s identity in a quest to discover his whereabouts. John has never married, never had a family and never really ventured further than his own front door. Without a computer, mobile phone or even a television, he lives in quiet solitude, designing puzzles for a living, under the nom-de-plume of ‘Ludwig’. However, filling the shoes of your identical twin is one thing - when your twin also happens to be a successful DCI leading Cambridge’s busy inner-city major crimes team the stakes are much higher.