BBC One comedy detective drama starring David Mitchell as John 'Ludwig' Taylor, a reclusive and socially inept puzzle-setter, who has never married; never had a family and never really ventured further than his own front door but who takes on his missing twin brother James's identity to try and solve what has happened to him. However as James is one of Cambridge's leading DCIs he finds himself unwittingly attempting to solve some of Cambridge's highest stake crimes.
Anna Maxwell-Martin also starred as James's wife Lucy who encourages John to pose as his brother to obtain some confidential papers from the police station, which is when he finds himself thrown in at the deep-end of crime-solving.
Paul Chahidi guest starred in Episode 3, playing security guard Adrian Tate who has booked himself and his wife a walking tour of Cambridge to celebrate their wedding anniversary. However things take a sinister turn when the tour guide is murdered and Ludwig and Lucy have to work out why someone would kill a tour guide they've only just met. Adrian and his wife find themselves at the centre of the investigation.
Other major names who guest starred in the series include Felicity Kendal, Derek Jacobi, Rose Ayling-Ellis and Karl Pilkington.