In 2010, the North Yorkshire village of Melsonby was left in shock when postmistress Diana Garbutt was found murdered in the post office she ran with her husband Robin.

At trial, the prosecution says Robin was stealing from the Post Office. Evidence from the Horizon system is a key part of the case against him.

Robin is sentenced to 20 years, but key evidence is missing. His DNA isn't on the murder weapon and data from the Horizon system can't be trusted.