Lucy Letby is the most prolific serial killer of our time. She is convicted of murdering seven babies and trying to harm many others. But there are serious questions about not only whether she is a killer at all, but whether there was ever a crime. In episode one, John Sweeney and Edward Abel Smith discover that all is not as it seems at the Countess of Chester Hospital, the place Letby is accused of carrying out her killing spree. Specifically, there were problems with the plumbing, meaning the neonatal unit where the babies died, was on a regular basis, literally full of shit.