The instant I mentioned a certain thing, her face changed color.

It looked like she'd deduced the situation from one word.

She wouldn't say anything, but...

Even I could tell from her face that it was something very important.

Probably

the killer's identity.

It all happened three days ago at a kappa lab.

Reisen and I had been working there recently, but that was the last day of our work.

What sort of work?

Visiting lectures, basically. The kappa had asked us to share our knowledge of Lunar science.

I talked about mechanical engineering, she about chemistry. It was a real hit.

After the lecture ended at 3 PM, the two of us started cleaning up.

We went to return the whiteboard we'd used in the lecture to the storeroom.

Suddenly, Reisen seemed to notice something and headed to the boiler room.

Sorry, I'll be right back. You put away the board.

Huh?