Whendunit

A new murder every day. Work out where everyone was, hour by hour. The guest left alone with the victim did it.

Lady Venetia Crane spent the whole evening in the smoking room of the SS Valdora. When the doctor fixed the time of death, exactly one guest was in there with her. Your job is to prove who.

How it plays

• A floor plan, a handful of guests and an evening, hour by hour.
• Each hour a guest either stays put or walks through one door. Nobody skips a room.
• Clues tell you who was where, who was alone, who got somewhere first, who never set foot in the library.
• Fill in the grid, then accuse. Every case has exactly one answer, and you can reach it by reasoning alone.
• Keep your working in the notebook beside the grid. Names, rooms and hours are a tap away.

The week

Gentle on Mondays, Steady midweek and Sundays, Tricky on Thursdays and Fridays, Fiendish on Saturdays. New to logic puzzles? The 1-minute walkthrough teaches the basics, and a 2-minute lesson teaches the "suppose" move that the harder days need.

Thursday to Saturday: when-dunits

On the hard days the doctor can't name the hour. You get a window instead: she died somewhere between 9 and 11. In exactly one of those hours, one guest was alone with her. Every other hour, the room was empty or crowded. Find that hour and you have your killer. Accuse them both: who, and when.

Stuck?

A hint shows where to look (30 points). The next step shows the reasoning (30 more). The answer explains every step. You start on 1000; time over par and wrong accusations cost too. Finish for a rank from Village Bobby to Chief Inspector, the killer's motive, and a spoiler-free result to share.

Open beta

It plays on phone and desktop, right in the browser, and saves as you go. Puzzles and features will keep improving through the beta, and your feedback decides how. Spotted something odd, or have an idea? Post it on the community board below. I read every message.

Whendunit is free to play. If you enjoy it, any donation is hugely appreciated: it keeps the cases coming.

Chris, Sir Percy's Lantern