On the 7th of May 2020, six-weeks after lockdown was announced, the source code for the UK's COVID-19 contact tracing app was published on GitHub. This is the story of how Open Source helped save lives. Come and learn about how we convinced the NHS to open source the app. What pitfalls there were. How we allayed security concerns. What went wrong. How we dealt with trolls. And why it was so important to be as transparent as possible. This talk asks if we did the right thing? Should have done something differently? Could we have been more open? Were the risks justified? Was being Open Source a help or hindrance? This is a personal recollection of a very strange period in health-tech history.