A few weeks ago, the British National Health Service was hit by a widespread and devastating cyber attack. This BBC documentary tells the inside story of one of the most challenging days in the history of the NHS. On the morning of May 12 the attack started. Appointment systems, pathology labs, X-rays and even CT scanners were infected - putting not just data but patients’ lives at risk. It became clear that all the data on an infected machine was now scrambled and only the hackers could unscramble it - but for a price. And if nothing was paid within a week, the hackers threatened to destroy all the data - forever.