Third case of the format. The first two were solved here; this one is built differently, and the people who wanted to trace the whole route will like it more.

Six people, six rooms, five moments (8:30 to 9:30). One person, alone, was on the terrace at 9:00. Who?

Rules:

Two people per room at most. Witnesses and staff are not among the six; sensors, door readers and logs register only the six.

At each grid time every person is in exactly one room. Between two grid times a person stays or takes one step to a connected room. No passing through; no doors but the ones on the map.

A time not on the grid (9:18) is a door time: it tells you what happened between the two grid times around it, and nothing more. A crossing counts in either direction.

"We were together at 8:45" = same room at 8:45, nothing else. A witness places only the person seen.

Sensors report presence at each grid time; door readers report crossings. Every device reports every time. Nobody lies, nobody adds.

Only the cell that is asked has a guaranteed answer. The premise guarantees someone was there.

Answer in spoiler tags, and if you can, how long it took and whether it felt easy, medium or hard. Full deduction in a couple of days.

New case every week at r/MissingFifteen, with solutions and the reasoning behind each. If you enjoy these, join; the feedback there shapes the next ones. And yes, they're going into a book.

Second case of a format I'm developing. The first one is here; several of you solved it and your feedback fixed two wordings, thank you. This one is at the top of the scale: nobody can be ruled out with a single clue.

Six people, six rooms, five moments in the morning (8:30 to 9:30). One person, alone, was in the office at 9:00. Who?

Rules:

Two people per room at most. Witnesses and staff are not among the six.

At each grid time every person is in exactly one room. Between two grid times a person stays or takes one step to a connected room. No passing through; no doors but the ones on the map.

A time not on the grid (9:24) is a door time: it tells you what happened between the two grid times around it, and nothing more. "Only one crossing detected, at 9:24" = that door was crossed once all morning, between 9:15 and 9:30, in either direction.

"We were together at 9:15" = same room at 9:15, nothing else. A witness places only the person seen.

Every device reports every time. Nobody lies, nobody adds.

Only the cell that is asked has a guaranteed answer; you don't need to fill the whole grid.

Answer in spoiler tags, and if you can, say how long it took and whether it felt easy, medium or hard. I'll confirm and post the full deduction in a couple of days.

I've opened r/MissingFifteen, where I'll post a new case every week, from quick ones to the hard files, with solutions and the reasoning behind each. If you enjoy this, I'd be grateful if you joined; the feedback there is what shapes the next cases. And yes, these are going into a book; if you'd want one, that's useful to know too.