Dr Hannah Fry explores how Artificial Intelligence is starting to transform healthcare beyond recognition, asking whether machines could ever replace doctors. She goes behind the scenes of British tech company Babylon Health, which has already persuaded 30,000 Londoners to quit their GPs and register instead for a digital service where patients use their phones to discuss their symptoms with an AI chatbot. To prove the accuracy of their online medics, Babylon prepare for a man-versus-machine showdown at triage and diagnosis. Will they prove a match for human GPs?