A wild Stab in the Dark

Folding knives - also known as jack-knives, flick-knives or pocket knives - originated in the middle ages. Cutlery was a luxury back then, so as soon as there were pockets (pouches which you hung from your belt) small knives were developed which could be carried in them. The 108 useful attachments (including that little pick for cleaning horses' feet) came much, much later.

This knife has a single steel blade set in an engraved horn pistol-grip handle, and was made in Sheffield in the 18th century. The knife handle would not have totally encased the blade - the nail nick we are so familiar with today was not introduced until the late 18th century.

When you are researching a detective novel, you spend quite a lot of time working out how to commit a crime. You have to enter the hearts and heads of people you wouldn't wish to meet on any dark night. And so I have started to think about flick-knives.

It began for me when I picked up Lt-General Adam Williamson's diary of 1722-1747. Williamson was a Deputy-Lieutenant of the Tower of London, one of the chief officers in one of the city's principal prisons.

Among the injunctions that the Earl of Lincoln, Constable of the Tower, put in place in Williamson's time was that:

"No wine [was] to be admitted to any close Prisoner in flasks, unless the covering of the Flask be taken off, and the bottle look'd through by holding a lighted Candle behinde it... no Liquor likewise to be admitted in stone Bottles, but the Liquor first to be poured out and the Bottles very carefully examin'd."

This got me thinking: rules tell you about what is happening that should not be. You don't order something to be done that everyone does as a matter of course: you make orders to correct faulty behaviour. If the officers in the prison are being told to examine bottles of drink sent in for prisoners, this is a sign that contraband has been smuggled in that way and has got past because of the guards' inattention.

And what is small, but deadly; might be wrapped in straw or a rag to stop it clinking; and might cause a terrible chaos were it to find its way into a prisoner's hand? A flick-knife.

And were they around in the 18th century, and small enough to fit in the bottle? Yes.

It is moments like this that start the brain ticking over as a story takes shape...