Pears puts the truth (such as it is) in the words of the real antiquarian, Anthony Wood, who explains that a fingerpost--like a pathognomonic sign--points to the only solution possible.

Perfect Poison: (averted) The poison used is a rather large amount of arsenic and what the reader is told of the victim's death doesn't suggest a lack of dramatic physical reactions.In the successive accounts, however, Cola's account is denounced as one that takes a great many liberties: the second narrator, Jack Prescott, finds Cola's memory "selective", while the third, John Wallis, goes much further, opening his account with the claim that Cola was: "the worst of men, the most savage of murderers, and the greatest of deceivers" -- and that his account was: "as fictional as Boccaccio and as unlikely as the rhymes of Tasso, though less finely hewn". Likewise, you might not want to overdo it with the tremendous volume and kinds of available medication. There is much said and little done, and the arrows of plot point in five directions at once with no real conclusion.

My history is far from good so I do not know if the historical facts were indeed accurate, but as the story progressed there were several twists and turns that I did not see coming - and that does not happen very often! A clever and well written mystery centered on a series of connected events as seen through the very differing persepctives of a handful of eye witnesses. It appears that the original convention was for A-road numbers to be in white on a black background and the converse arrangement for B-road numbers, although there are few fingerposts with this as their current scheme.Sometimes these instances of the fingerpost meet us accidentally among those already noticed, but for the most part they are new, and are expressly and designedly sought for and applied, and discovered only by earnest and active diligence.