"This is a book about prion diseases - what they are, what causes them, who they afflict, how we might cure them and how we found out what we know about them." This bland statement on page xxv of the introduction gives no clue to the unique manner in which Mr D T Max narrates an account that had me spellbound. Prions have fascinated researchers as they cause diseases in animals and man but cannot be shown to replicate like viruses or bacteria and cannot be destroyed by any of the means used to kill micro-organisms. (Stanley Prusiner - of whom more later - was searching for a name as catchy as "quark" for the factor responsible for these diseases and came up with the term 'prion'. Nature commented that it was "a rather tortured acronym for proteinaceous infectious particle".)