[short story] Lights in the dark

This is chronologically the first short story I publised in English, even if it wasn't the first I began writing.

They were sleeping when the lights came through their window. They were not blessed with great wits or the gift of logical thinking. What they were given was great eyes instead: they had a condition called abnormal tetrachromacy, which meant that they had limited infrared-vision. When I learned about it from them I, as I have been always fascinated by colors and color deception, had to ask,

"what does infrared look like?"

"You know, like red, just... warmer", they told me which, I suppose, made sense, but it does not help me to understand the sensation.

I am well aware that neither you nor I will never be able to experience seeing colors outside of our visible spectrum, but they can see beyond it. And what they saw on that night was something truly... something.
I was with them when they opened their window to let some fresh air in. It was a the first hot day of the summer; ensuring proper airflow was anything but a useless task. As we went to sleep I remember having trouble falling asleep, my sheets were wet from sweating and my pillow felt like my head rested on mud, so I got up to take a break, had a drink and went out to the balcony hoping that there is wind or any minor air movement that could help to cool down my body. And that was when I heard them yelling "Close the window! Now!" I instantly went back into the tiny hell we called our home and looked at them, terrified.

"What happened?" I asked, "are you alright?"

"It hurts, it hurts so much..." they said with visible pain in their voice.

"What hurts? Another bird flew in and attacked you?" I tried to see what they were doing, but my eyes had not yet accommodate the darkness of their room.

"No, the... the..." they struggled to make comprehensible sounds, "eyes." They took a deep breath and continued, "there was a light..."

I have to admit I had no idea what they had saw. "What light? I didn't see anything. And how did closing the window help when there is a light?"

"It was infrared," they replied angrily and with fear. "How could've you seen that?!" They almost broke down crying, but I had to know, so I pushed further:

"Where did it come from? Shouldn't I have to feel it? I was on the balcony—" They interrupted me.

"It was directed, directed at this room!" they said, now crying. "And it's still there."

I looked at the window, but I saw nothing out of the ordinary, only the stars, faint street lights from afar and a car going on the street. "Are you sure it wasn't just a..."

"No!"

I wished to know more, but I decided not to force this conversation on them. "Okay, okay, so what you do know?"

The room begin to feel hotter as they answered, "I... I don't know. Do you think, that are they might be th—"

"That isn't possible. But if it makes you feel better, I can—" They didn't let me finish.

"Yes!" they said with a hint of hope in their voice, so I did some precautionary measures and went back to sleep. At least my bed is dry now, I thought.

The next morning I woke up from a peaceful dream, well rested, ready for the day. I decided that whatever happened last night must have been a dream or a mix between dream and reality — given how tired I was, it would not be surprising — when I saw their door. It was hard wood and heavy duty, still sealed from the outside, they must be still inside. I broke the tape I had crudely put on it and opened the door; the room was empty. Where they are? As I recall, their sheets were gently cast aside, which indicated that they left the bed normally, not in a hurry, yet their slippers were still under the bed. Then I moved onto the window, also sealed from last night. It isn't possible, where are they, what happened here, how did they left? I examined their room more thoroughly, looking for hidden vents and trap doors, but there was nothing. The door was sealed, the window are still sealed, there are no other entrances, there aren't any hidden ways... I went back to the door and took another look at the tape, it did not feel as if it had been removed before I did, and the one on the window are still in place, intact, there was no way it had been taken off and put back. I had no choice but to admit that they were gone and so was I.

On that day I packed all of my belongings, save for a few books on chromatics, and left the apartment, let our landlord know I was no longer staying there and slept at a friend's until I found my own. Even though my memories of that night are blurry and incomplete, I am certain that whatever took place was not something I will ever forget nor be able to explain. I frequently think of them being there, fearing the light, for their lives, not being able to help themselves. And while I often find myself thinking "what else could've I done?" I am no longer seeking answers, for I fear what I might end up finding.