The Number He Already Had

Dear friend,

The riddle first, as the tradition demands. I set this one in your own century, the old town having no letter that could be altered without the seal showing it, and the whole difference between these two men was a telephone number written down nine years before it was wanted.

Two fencing contractors in your own century, the same vans and the same timber yard.
Both had a note from that yard in the same September week, the bank having changed.
Both notes sat in the same thread as the invoice and quoted its number correctly.
One paid on the Thursday, as he always paid, promptly and in full.
One turned to a number he had written in his book nine years before.
Same trade, same note, same yard. Which man paid for that timber twice?

Hold your answer. Story time.

The Story

Both men put up fencing out of a van, and both were good at it. The same smell of creosote in the back, the same thump of a post rammer in a wet garden, gravel boards stacked against a wall at eight in the morning. Both bought their timber eleven miles out, from a yard whose office is a portable building beside the gate and whose orders the same woman has taken for a decade. Posts went out on a delivery note, the invoice came by machine, thirty days to pay.

In the second week of September each man had the same message. The yard had changed banks. Here were the new details, and would he kindly use them for the invoice just sent. The note sat in the same thread as that invoice, directly beneath it, quoting its number and its date and the delivery note with it, signed off in the short manner of a busy office, carrying at the foot the small photograph of the yard gate that every message from there had carried for years.

The first man paid on the Thursday, which is when he paid things. Four thousand two hundred and sixteen pounds, into the new account, from a lay-by with the engine running. Three weeks later the woman from the yard rang about an unpaid invoice, in the mild tone of a person expecting an oversight. The money had gone on the Thursday afternoon, the account was emptied by the Friday, and the bank was very sorry. He paid the yard a second time, out of money set aside for a tipper.

The second man read the same note and thought nothing suspicious of it. What he had was not suspicion. It was a rule, on a strip of card taped inside the lid of his paperwork box: no change to where money goes without a voice on a number we already had. So he turned to the back of his order book, where the yard's office number was written on the day the account was opened, and rang it. The bank had not changed. By the Tuesday the yard had turned its passwords over and warned its other customers, two of whom were already on their way to pay.

Be fair to the first man. He was prompt, and promptness in paying is a good habit. He did not check the note because there was nothing in it to check. No word of it was wrong except one line, and that is the whole craft of the thing. Nobody forged a letter. Somebody sat inside another firm's mailbox and altered the account number on a true one.

The Lesson, Since You've Earned It

An instruction that arrives by machine is a claim and never an authority, so any claim that moves money, or changes where money goes, is confirmed by a voice on a line the claim did not come down. Not by replying to it. Not by ringing the number printed inside it. On a line you held before the note existed.

Begin with what such a note is made of. Every mark of authority on it can be copied at no cost: the name at the foot, the manner of writing, the photograph of the gate, the invoice number, the figure to the penny, the thread with your own last reply underneath. A man who has read a mailbox for a fortnight has all that for nothing, and the thing no stranger could guess besides, which is that you expect precisely this invoice from precisely this firm this week. In my century a swindler had to counterfeit a letter and get it into a mailbag. In yours he need only amend a true one, and the amendment is eleven digits long.

Which tells you where the check must sit. Not in judging the note, since the note is perfect and will defeat you, but outside it, in something you had before it came: a number in your own book, written when the account was opened, dialled by you. That is the one article the man in the mailbox cannot reach. The accounts your trade runs on want guarding in the same spirit, as I argued in the letter about where your passwords are sent.

Then consider the hour at which these notes arrive, which is never idly chosen. Late on a Friday. The week your invoices are already overdue. The morning two gangs are waiting on timber. Urgency is not an accident of the message, it is the mechanism of it, since a hurried man does not weigh a thing, he processes it. Which is why the answer is a rule and not a resolution to be careful. Care is the faculty you have least of on the days you need it most. The rule costs nine minutes when it is wrong, which it will be nearly every time, and nine minutes against four thousand pounds is not a sum anybody need do twice. So it goes wherever a machine acts faster than a man can think, as the trader who sent eight hundred messages at once found out.

Write it where the money actually leaves, which is not only your own hand. It is a wife at a kitchen table on a Sunday, a bookkeeper two days a week, a lad with the card for the fuel. A rule kept in your head protects one payer, and the thief needs only the other.

Two cautions. The first is that the check is on the instruction and not on the person, so do it cheerfully and say what you are doing. There is no insult in ringing a yard of nine years' standing to confirm a change its own office will be glad you doubted. The second is that nothing inside the note counts as an answer: a new bank, an old account closed, a request not to use the old details, these are the words of the very thing you are checking.

Three questions, for the week in front of you:

1. Who here can send money out, and what would each of them do with that note? Count everybody with a card, a banking password or the authority to pay an invoice, yourself included. If one of them pays it on the Thursday, you have this week's work.
2. Where is the number I would ring, and when was it written down? For your three largest suppliers. A number taken off the invoice in front of you is not a second line, it is the same line.
3. What is the largest sum that can leave here without a voice? Name the figure today, in pounds, rather than leave it to be discovered.

The Answer to the Riddle

The same vans, the same yard, the same note in the same September week, quoting the same invoice correctly in the same thread. Which man paid for that timber twice?

The first, and not for want of sense. He paid twice because he was asked a question he could only answer from inside the note, and inside the note everything was true. The second answered it from outside, on a number written down nine years before anybody thought of robbing him. He did not judge the note better. He refused to be its only witness.

The verse:

The thief no longer forges, for a forgery can be read,
He waits inside the mailbox and he alters one true line.
So keep the number given on the day the account was opened,
And let a voice you knew before the note say where the money goes.

Until next time. Go and write that one line where your invoices are paid, and put the office number of your largest supplier beside it.

P.S. The traffic runs the other way as well. One day a note will go out in your name, to your customers, with somebody else's account number in it. You cannot prevent it, but you can make it fail. Put one line at the foot of every invoice: our bank details do not change, and any message saying otherwise should be checked on the number you have always used for us.

Also in the archive: Sent in His Name, The Message Nobody Missed and The Copy He Never Needed.