What it says on the box, really. This is a straightforward compilation of the events of those two great London disasters. The section on the Plague is rather longer, telling of the rapid rise of the epidemic, the treatments that were proposed and the desperate measures taken to control, or contain, the disease. There are some chilling anecdotes: healthy individuals boarded up in their houses with dying plague-victims; the symptoms of bubonic plague; a plethora of nostrums including philosophical gold, 'of Elizabethan coins if you can, it is of ye best'; the determination of some towns to keep the Plague out at any cost; and even hints of necrophilia (but only hints: this was written in 1961). Apparently, this is the book that first suggested a connection between the nursery rhyme 'Ring o'Roses' and the Plague.
The account of the Fire is rather shorter, and relies more heavily on Pepys' Diary. Leasor gathers a variety of sources and concludes that not enough was done in the early stages:
The night burned far brighter than the day; the fire was many times stronger than it had been only a few hours earlier, yet still nothing drastic was attempted to quench it; and still those not immediately affected did not realise that it could possibly affect them. There have been worse cases of official inertia and private folly, but not many and not much. (p. 213-4)