DI Ruth Calder investigates the killing of a retired social worker. Plus: the final episode of scandal drama The Hack. Here’s what to watch this evening DI Ruth Calder investigates the killing of a retired social worker. Plus: the final episode of scandal drama The Hack. Here’s what to watch this evening 9pm, BBC One One minute you’re moaning to your colleague about a rubbish first date, the next you’re sifting through frozen fish for illegal drugs. It’s all in a day’s work for DI Ruth Calder (