Ciphers and mechanical hiding

A cipher is a lock, and the only interesting question about a lock is who holds the key. These are the physical ones — the sort that need an object rather than arithmetic — so that solving them is something the players do with their hands instead of something one player does in their head while everyone else waits.

Hiding writing mechanically

The impression in the pad

Write hard on the top sheet of a notepad with a ballpoint, tear that sheet off and throw it away, then hand over the pad. The page beneath carries the writing as indentations, invisible until somebody shades across it with the side of a pencil and the letters appear in white through the grey.

Two details make it work. Press much harder than feels natural, since the indentation has to survive being carried to the table; and write something worth the effort — an address, a name, a single number — because a whole paragraph in reverse-relief is slow to read and the effect does not improve after the first line.

Mirror writing

Print the message flipped horizontally and it is legible in any mirror, any phone camera and any shop window. Nobody will be stuck for long, and that is the point: it is a lock that opens in ten seconds and still makes the players do something. Use it for the note left by a person who wrote it in a mirror, or for a page meant to be read by holding it up to a polished surface in the room you are describing.

A watermark held to the light

Write in very dilute ink, or glue a thin cut-out between two sheets, and the mark stays invisible flat on the table and appears the moment the page is lifted towards a window or a candle.

Microprint

Set a line at two or three points and it prints as a grey rule that nobody can read without a magnifier. Hide it along the border of a certificate, under a signature, in the frame of a map. Then give the magnifier out separately, an object in its own right, and the table will start examining everything you have ever handed them — which is a habit worth more than the message you hid.

The scytale

Wind a long strip of paper around a rod, write across the turns, unwind it, and the letters are scattered nonsense. Wound onto a rod of the same diameter they line up again. The beauty of it is that the key is not a word or a number but a thickness — a staff, a bottle, a chair leg, a particular candlestick — so the party can hold the message and the key at the same time without knowing they have both.

Make it from a strip cut along the length of a sheet, wound in a tight spiral with no gaps, and write in capitals straight across. Test it with the actual object the players will find, not with a pen of about the same size, because a millimetre of difference turns a solution into an evening of frustration.

Physical ciphers

The Cardan grille

Take a sheet of card the size of the letter and cut windows in it. Lay it over the letter and the words showing through the windows are the real message; lift it away and the letter is an innocent note about a shipment of wool. Write the letter around the hidden words rather than the other way round — put the secret words on the page first, in the positions the windows will fall, then compose something ordinary that contains them.

The grille is the most satisfying of these because it has two states and both are readable. Give the players the letter early, let them take it at face value, and deliver the grille three sessions later — from a dead man's effects, from a safe, from the sender's own desk.

Two transparencies

Print half the image or half the text on one sheet of overhead film and the other half on a second, each meaningless alone. Laid over each other and aligned — by a corner mark, a border, a pair of holes — they resolve into a map, a face or a sentence. Split them between two NPCs, two factions or two halves of a party and the fiction does the rest.

The book cipher

A list of number triplets — page, line, word — and a book that turns them into a sentence. It is unbreakable without the book and trivial with it, which makes the whole puzzle a hunt for a specific edition of a specific volume, and that is a far better scene than any decoding. Choose a book the party can plausibly find in the fiction, and make sure the copy they find is the one you used.

Keep the message to a handful of words. Ten triplets is a scene; forty is homework, and the tenth lookup is not more interesting than the second.

A knotted cord

The message lives in the number of knots and the distance between them, read along the cord — a quipu, or a rosary somebody counted differently. It is the only handout here that is not paper at all, it survives water and fire, and a party will carry it for months without realising it says anything. Give the legend later, or hide it in a carving somewhere; the cord alone is an object, and the object is enough to start with.

Interactive

All of these are destructive, so print two. One for the table and one in the folder, because a handout that only exists in the state the players left it in cannot be shown to the person who missed the session.

A torn letter as a puzzle

Tear the letter by hand into six or eight pieces — not twenty, and never with scissors, because a straight cut looks like a jigsaw and a tear looks like someone was angry. Hand the pieces over in batches as the party searches: three from the fireplace, two from a coat pocket, the last one from somewhere they have to go back for. The reassembly happens on the table, in front of everyone, and the missing piece is a plot hook that needs no explanation.

Age the sheet before you tear it, or the torn edges will be brilliant white against a yellowed face and the whole thing will read as new paper damaged this afternoon. And write the letter so that the surviving pieces still say something on their own: half a sentence about a meeting is better than a complete sentence about nothing.

Shredded strips and a blacklight

A straight-cut shredder leaves strips a patient table can reassemble in twenty minutes, which is an entire scene of its own if the fiction gives them a reason to sit in an office doing it. Put a second message across the strips in UV pen before you shred, and the reward for reassembling them is not the text they expected but one nobody knew was there.

Twelve strips is a puzzle, forty is an ordeal. Shred a half-sheet rather than a full one, and number the backs faintly in pencil if you ever want to reset it for another table.

Rice paper and dissolving paper

Edible rice paper takes an inkjet print and dissolves in water in seconds; dissolving paper sold for magicians does the same faster. Either turns reading into a choice — the message exists once, and whoever is holding it decides whether the rest of the party sees it before it goes into the glass.

It is fragile in a way ordinary paper is not: damp hands mark it and a pocket destroys it. Carry it flat between two sheets of card and hand it over at the moment it matters.