Cold cases & unsolved murders 3 cases open · posted worldwide
Unsolved case file games,
hand-packed in Britain.
A box of real paper — letters, photographs, telegrams, coroner's notes, pages that need decoding — and one murder nobody ever proved. No app, no dice, no monthly subscription. Just the evidence, a sealed solution, and as long as the mystery takes you.
- Free UK delivery on any order with a case file in it
- Hand-packed in Grimsby
- 14-day returns on unopened cases
The short answer
What an unsolved case file game is
An unsolved case file game hands you an investigation instead of telling you a story. What arrives is the file itself — witness statements, photographs, telegrams, coroner's notes, coded pages, the occasional personal effect — and nowhere in it does anybody name the killer.
You'll find the same thing sold as murder mystery case files, or as cold case games. It's one idea under three names: a crime nobody closed, handed to you as paperwork rather than as a plot.
There's no board and nothing to download. You read, you cross-reference, you argue civilly with whoever else is at the table, and when you're ready you break the seal on the solution and find out how close you got. Every Cosykiller case is a real historical setting, researched for period detail and printed in a limited run, so the paper in your hands looks like paper somebody filed away and forgot about.
- 01
Open the file
A letter from Fairhall & Brett Inheritance Recovery — the fictional investigators who brief you — explains why the case has landed on your table and what nobody managed to prove at the time.
- 02
Work the evidence
Read in whatever order you like. Cross-reference the statements against the dates, decode what's coded, and keep notes. Everything you need to name the killer is somewhere in the box.
- 03
Break the seal
When you can say who did it and why, open the sealed solution. It's written as a final piece of the story rather than an answer key — satisfying whether you got there or not.
Currently open
The unsolved cases
Each one is a self-contained murder mystery, written by the crime-writing team behind Cosykiller and packed by hand in Grimsby. Print runs are limited on purpose — when a run sells through, that case closes for good.
2-4 hours
Europe 1946
Shadows in the Gallery
A body discovered in a bricked up cellar unlocks the start of a cold case investigation.
9-12 hours
Mexico and America 1950s-1980s
The Secret of Site Q
A body uncovered at an abandoned campsite in the dense Mexican rainforest reveals there was more to a simple tragedy.
6-11 hours
Simla, India 1934
An Inheritance of Murder
An heir hunter team reaches out to you to ascertain if you are the long lost heir of an English Estate.
Closed files 5 earlier cases have sold through their print runs — Murder at Marlborough House, The Hidden Listener, The Legend of Ching Shih, The Curse of Humanrah, Cosykiller Origins: Virginia Steele. Their files stay in the full case archive.
One sitting
Unsolved mysteries in a smaller box
If a full case file is more than you want to take on tonight, the puzzle boxes are the same idea at a fraction of the size. A deck of stand-alone puzzle cards, each solvable on its own, all of them feeding one final answer that stays sealed until you're ready.
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Puzzle box Modern-day espionage thriller
Mission Rogue Protocol
A skyscraper, a hostage situation, a device counting down. Pick the locks one puzzle at a time.
£12 See it -
Puzzle box 1940s wartime Britain
Homefront Heroes
Crack the entrance puzzles, learn the password, and decide which side of the wartime black market you're on.
£12 See it -
Puzzle box Baskerville Hall · early 20th century
Sherlock Holmes & the Return to Baskerville Hall
Holmes is back at Baskerville Hall. The house is full of clues, ciphers and statements that don't quite line up.
£12 See it -
Puzzle box Aboard the S.S Kipper
Space: System Error
Captain Plannet has gone missing aboard the S.S Kipper. Decode the alien alphabet, unlock the C.L.E.D., find out where he went.
£12 See it
Where to start
Pick by the evening
you've actually got.
The difference between the three isn't difficulty so much as appetite. All of them are rated 14 and up, and all of them can be worked solo or around a table.
- 01
One evening
A puzzle box
A deck of stand-alone puzzle cards, one locked answer at the end of them. No series to follow and no characters to keep straight — the cheapest way to find out whether this kind of mystery suits you.
From £12 See the boxes - 02
A long evening
Shadows in the Gallery
A complete cold case in a single box — a body found behind a bricked-up cellar wall in 1946, and twelve documents that disagree with each other. Playfair, knock code and Caesar ciphers, so bring a pencil.
£45 Open this case - 03
Several sittings
The Secret of Site Q
The full-length investigations — twelve episodes of evidence, delivered in one go rather than drip-fed monthly. Spread across a few weekends, with notes, a wall and somebody to argue with.
£285 Open this case
In their own words
What solvers say
“I recently completed the "An Inheritance of Murder" mystery, and I am officially in awe of the folks at Cosy Killer! The story line was intriguing, and the materials in each box were elaborate and contributed to the aura of mystery. Most importantly, the puzzles, clues and ciphers were varied and complex. But don't worry — if you get stuck, there is a community of nice folks with whom you can brainstorm and from whom you can get hints!”
“I received my first box in mid Dec and have only just sat down to start reading but so far I can get a sense of fantastic attention to detail from the turmeric pages, chai tea and the book cover to the faded bits. Can't wait to begin to make sense of it all!”
“I am only three episodes in but the storyline is awesome and very gripping. I didn't want to stop reading! You get very authentic items and they pay close attention to detail. Very impressed!”
Before you buy
Questions we get asked
What is Cosykiller?
A hand-packed murder-mystery case file delivered to your door. Each box contains clues, keepsakes, ciphers and mementos — like an Agatha Christie novel where you play Miss Marple. No conclusions are drawn; the puzzling and detection is up to you.
I'm new to Cosykiller — where should I start?
Start with An Inheritance of Murder. It's our gentlest case, built for puzzle-minded beginners — Braille, letter-to-symbol substitutions and one-time cipher pads. The Secret of Site Q is the step up: a longer, cross-referencing investigation that's challenging but solvable. Shadows in the Gallery is our most advanced case, layering Playfair, knock code and Caesar ciphers across a post-war art theft — do it once you've worked one of the others.
What's inside a Cosykiller box?
It varies by case, but every box contains a cover letter from Fairhall & Brett Inheritance Recovery — the fictional investigators who brief you on the case — followed by the documents like photographs, ciphers, maps, letters, military archives, telegrams, postcards, and other personal effects collected during the investigation. Some cases include dried botanicals, spices, theatre programmes and small physical objects. Each case is a complete story, with the final solution provided at the end. Nothing to download or sign into.
How long does it take to solve a case?
2-4 hours for our single box solves, and between 6-11 hours for some of our longer games. Length of time also depends on the number of players, and how much you like to re-read and how quick you are at spotting and solving ciphers. Most people spread a case over two or three evenings. You can pause whenever you like — put the lid back on, come back next weekend. Nothing expires.
Can I play solo, or do I need a group?
Both work well. Every case is designed to be solvable on your own — no mechanic depends on a second reader. That said, two to four players is where a case shines, because half the fun is arguing civilly about motive over a drink.
Where do you ship to?
Worldwide, by tracked post. UK delivery is free on any order with a case file in it and takes one to three working days, and the UK price includes VAT with nothing further to pay. Orders outside the UK may pick up import VAT or customs duties on arrival — that's out of our hands and depends on your country.
More on the full FAQ, shipping and delivery, or write to us directly.
The file is openNobody has closed it yet
Somebody got away
with it. Prove it.
3 unsolved cases on the shelf and a shelf of puzzle boxes beside them. Pick the one that suits the evening you've got — or tell us who it's for and we'll pick for you.