A time of horror has come to London. In one terrible summer, more than 15% of its population will perish. As the bubonic plague ravages London's streets, mercilessly plucking up victims and filling the plague pits with corpses, 13-year-old Alice Paynton records the outbreak in her diary. "It seems that in the past week 700 people have died of the plague. So the plague has well and truly come to London ... One of the houses in the next street had a red cross painted on the door. Above the cross someone had chalked Lord Have Mercy Upon Us." Alice's chilling diary brings alive one of the darkest moments in British history: the Great Plague of 1665-1666.