Dr Michael Mosley ends the series with a look at poisons, exploring the turning points when scientists went from finding antidotes to poisons to applying poisons as a cure - celebrating the eccentrics and mavericks whose breakthroughs were to pave the way for some of the most striking treatments of modern medicine. Of the medicines explored in this series, those that are derived from poisons are perhaps the most extraordinary. The story of turning poisons into medicines encompasses the planet's most deadly substances, in which we turned killers into cures.