It is hard to imagine a more compulsive opening than Waller's vivid account of how, on 14 July 1518, Frau Troffea of Strasbourg began a violent, joyless dance that continued for six days. Even more oddly, she infected others with the same bewildering malady.
We might imagine it as a colourful medieval oddity, like the dancing in Bergman's Seventh Seal, but it was "more shockingly disturbing than most can easily imagine." Dismissing the usual explanation of ergot poisoning, Waller blames collective hysteria inspired by St Vitus's Day (15 July).
A saint "who healed and cursed by turns", Vitus tortured victims with ceaseless dance. Choreomania only took hold in the Rhineland where this belief held sway. Brilliantly exploring a medieval mania, Waller notes that clubbers may be "the chemical equivalent".