The short version About Cosykiller
We make murders
in a box.
Cosykiller case files are narrative murder mysteries you solve on your own terms. We write the story, research the period, source the paper, commission the photography, print the documents, pack the boxes ourselves, and post them from a small workshop in Grimsby.
Where we came from
Fifteen years of other people's murders
Cosykiller is part of RHG Events Ltd — a family of small brands that have spent the last fifteen years making murder-mystery games for parties, holidays, schools, stag and hen weekends.
Some of those games are broad and silly. Cosykiller is the quieter one — for the kind of people who think the highlight of a Sunday is a slow argument about motive.
- 15 Years writing mysteries
- 5 Cosykiller cases on the shelf
- 40+ Countries we've posted to
What Cosykiller is trying to be
The richest box of paper you can buy
Every case we post aims to be the most tactile, most cross-referenceable murder mystery you can fit in a single box. Four principles we never compromise on.
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The paper feels right
Letters on laid writing paper. Telegrams on telegram stock. Newspaper cuttings on actual newsprint. The texture is half the clue — we refuse to print everything on the same white card.
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The period is researched
Victorian vocabulary, 1920s stamps, 1950s postal marks, the right typeface for the right decade. If it sits in the box, someone has argued about whether it would have existed in that year.
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The objects are evidence
Dried botanicals, coins, buttons, matchbooks, pressed flowers. They're not props and they're not packaging. If it's in the box, you're meant to read it.
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Everything cross-references
A name in a letter turns up on a passenger manifest. A date on a telegram matches a newspaper headline. Solving is the joy of noticing — and we write backward from the solve.
Why Cosykiller
Three things
other case files don't do.
Case-file games are a busy shelf. Here's what ours do that the others mostly don't.
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01
Six to eleven hours of mystery
Most case-file games run three or four hours. Ours run six to eleven. Long enough for false trails, dead ends, and the one extra document that makes you change your mind on the solve.
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02
Eighteen years of murder writing
We've been writing mysteries for parties, schools and stag weekends since 2008 — first as Red Herring Games, now as Cosykiller too. The plots aren't sketches. They're proper whodunits with motive, means and an alibi worth testing.
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03
No app, no website, no expiry
Every answer is sealed in the box — the final solution, the three hint envelopes, and the "things most people missed" page. Nothing to download, no account to sign into, no support URL to go dead in 2031.
Who "we" actually is
A small team in Grimsby
Five people with particular obsessions, a workshop full of paper stock, and a kettle that never stops.
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The writer
Argues about Victorian vocabulary. Reads five period novels before writing a line of correspondence.
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The illustrator
Specialises in forged period documents — letterheads, telegrams, letters of credit, municipal stamps.
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The sourcers
Two people who spend too long on eBay sourcing vintage stamps, ticket stubs and matchbooks we can base our replicas on.
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The packer
Emma hand-wraps every box with brown paper and kitchen string. The string is not for show — it keeps the lid down.
We reply to emails — usually within a day, sometimes two — at hello@cosykiller.com.