Britbox’s miniseries adaptation of Agatha Christie’s Towards Zero is familiarly digestible, but also a little stale — until Rhys’s Inspector Leach shuffles into Gull’s Point. Photo: BritBox How does one update an Agatha Christie story? Kenneth Branagh has his increasingly elaborate Poirot mustache. Rian Johnson uses his Christie pastiche to swipe at the Trump-coded megarich. And now Agatha Christie’s Towards Zero has a secret weapon that shakes it out of its very staid, very proper presentation