Professor David Harrison is Honorary Consultant Pathologist at Lothian University Hospital NHS Division and Professor and Head of Pathology at the University of Edinburgh. We tend to assume that cell death is a bad thing, and indeed this is often the case. However, sometimes individual cells are sacrificed for the greater good, for example, killing virus-infected cells. But what happens when a cell that should die doesn't? Professor Harrison investigates. This lecture is part of the Medical Detectives, a series of public lectures that show how keen detective work is still essential for 21st century doctors: http://www.ed.ac.uk/news/events/medical-detectives/ Recorded on 6 October 2011 in the Anatomy Lecture Theatre at the University of Edinburgh.