As Alyx held her mother's hand and the two of them approached a stop for the transit system, the little girl remembered a heated conversation her parents had had a few days earlier, or rather, the last sentence of a heated conversation. The fact that they were headed to school caused her to remember it. Alyx looked up at her mother.

'Mom, why did you tell Dad Black Mesa was no place for children?'

That caught Azian off guard.

'What do you mean, baby?' she replied cautiously.

'A few days ago I heard you say Black Mesa was no place for children. You said it to Dad.'

Alyx had been living with her parents in Black Mesa for as long as she could remember. She could see nothing wrong with the place herself.

'Your Dad and I just had a disagreement, that's all.'

'Why?'

'Because….' Azian had to think for a moment. 'Because Black Mesa Elementary isn't like other schools, Alyx. Other schools aren't right in the middle of a research facility. Other schools have wide-open spaces to play in, the teachers aren't scientists, and the children who go there aren't all sons and daughters of the scientists that work here. I just thought it might have been better for you to go to a real school.'

'But I like it here.'

'I know baby, and so does your father. That's why we'll probably stay here, at least for a while. Your Dad said we might consider moving after today's big experiment, but I think that after it's done he'll be given another important project to work on and he'll want to finish that.'

Alyx sensed something in her mother's tone.

'Don't you like Black Mesa?'

'I think I'd like it more if I was a scientist like your father, but here I just feel out of place. You know I'm not a scientist or a security guard or anything like that. I liked it here at first but I'm starting to miss life on the surface. Maybe all I need is a bit of a holiday from Black Mesa, that's all.'

At this point, the automatic tram had arrived and mother and daughter had stepped onto it. It was completely empty but for them. The journey to Alyx's school was always quiet. The little girl was the only child in her class whose father worked at Anomalous Materials, so the tram ride from the Sector C dormitories to the school only ever involved two people: Alyx and Azian. Alyx was still too young to make the trip by herself, but she would be old enough soon. As long as you remained inside the tram, journeys through Black Mesa were quite safe.

Alyx thought about what her mother had said. She had never considered the possibility of taking a vacation from Black Mesa. The research facility was her whole world. She saw no need to leave it. She even knew what she wanted to do when she grew up. She would be a scientist at Anomalous Materials like her father.

In no more than ten minutes after they had boarded the tram, it came to a stop at their destination. As on every weekday, Azian and Alyx went to the elementary school's entrance where children played and parents talked. This area was illuminated with natural light to make it look more like an ordinary, habitable school and less like a sterile research facility. Above where they stood were the open sky and something which you only occasionally saw at Black Mesa: a red-rocked canyon which let in the pitiless New Mexico sun. It allowed the school entrance to resemble something more like a park. Plants and small trees were neatly placed here and there, as were benches, though most of those waiting for the morning bell to ring were standing, or in the children's case, frolicking, in the shade.

Azian conversed briefly with those other parents she knew, while Alyx joined her classmates. When the nine o'clock bell tolled, Azian hugged Alyx and watched her leave through the school's double doors with the other kids.

Azian took the transit system alone back to Sector C, trying to tune out the inevitable prerecorded announcements that prated through the whole ten-minute journey back to the dormitories.

Not every scientist at Black Mesa had children, so Alyx's class was relatively small. There were no more than twenty kids, most of them aged either four or five. Like her mother had told her that morning, the teachers at Black Mesa Elementary were scientists who work part-time. Because of this, many of the class's lessons involved science but were simplified, so that they could be understood by young children. That suited Alyx just fine. Whenever she heard her father talk about his work she would always listen, spellbound. Eli was truly passionate about what he was doing in Anomalous Materials, and more than that, it was clear he found his work exciting. Alyx was too young to understand what his work in Sector C involved, but Eli's enthusiasm, his intellectual fervour, really had an effect on his young daughter. It was the main reason for her wanting to become a scientist like him.

Alyx's day began with a simple lesson on the basic building blocks of life. Their teacher talked about atoms, about how at one point everybody believed they were the smallest and most basic building blocks of life. Then scientists discovered that they could be divided and were made up of protons, electrons and neutrons.

Alyx could see many of her classmates were fidgeting or looking out of a window at the red rock of the Black Mesa canyon outside. She also felt a little distracted, not because the lesson bored her, it didn't, but just because she had heard about atoms before. Her mind couldn't help but wander to thoughts of her father. Over the past few days she had watched Eli become more and more distracted, and this very morning he had been as perturbed as he was ever going to get. Alyx knew the cause of it too. Eli had not spoken about it with his daughter, but she had heard him talking about the source of his worry to her mother.

After she had been put to bed, Alyx had edged silently down the stairs to eavesdrop on her parents, something she did whenever she couldn't get to sleep. Much of the conversation went over her head. She had no idea what "exotic matter" was, nor "quantum tunnelling" or the possibility of a "Resonance Cascade", though Alyx did understand the gravity and fear in Eli's voice.

"Resonance Cascade." It was a nice-sounding phrase. It made Alyx think of something like gentle rain or hailstones falling from the sky. But the way her father said it made her think of something much more terrible, like a lightning storm or a big fire. Neither of those things could happen at Black Mesa, she told herself. They were in the desert, there was no wet weather. And there could be no fire. Everything at Black Mesa was steel, stone or concrete.

Nonetheless, late at night, when Alyx had grown tired of eavesdropping or Eli and Azian's conversation had changed to a much lighter subject, Alyx would crawl back upstairs to her bed. However, Eli's fearful words would stick in her mind until sleep overpowered her apprehensive thoughts.

Alyx was snapped out of her reverie all of a sudden. The strip lights on her classroom's ceiling blinked off and were replaced by a flashing red from a light she had never seen illuminated before. It was accompanied by a terrible whooping alarm and a robotic voice which called out:

Danger—Danger. All—personnel—evacuate—facility—immediately. This—is—not—a—test.

There were outcries of surprise and fear from Alyx's classmates, and for several seconds there was pandemonium in the small classroom. Many children started to cry in panic, others seemed to be enjoying what was happening, exhilarated by the sudden anarchy that had descended onto the classroom. Alyx was feeling a mix of both reactions and wondered what had caused the alarm. It couldn't be something to do with her father's experiment, could it?

Presently, their teacher collected herself, taking a moment to recall the evacuation procedure, and managed to shout over the braying alarm.

'Everybody form a line in front of the classroom door', she yelled.

Those children who were not entirely panic-stricken, and could hear their teacher's voice, did what she said. Others had to be helped out of their seats and ushered toward the gradually forming queue at the door. Alyx was third in line. She was eager to emerge out into the halls of Black Mesa and see how the scientists and security guards in the rest of the facility were reacting.

Now another alarm had started. It had a much longer report. The two repeating sounds were terrifying, not just for children, but for anyone working at the facility.

Looking back at her distressed classmates, Alyx almost felt like crying herself. This no longer felt like an exciting adventure. Something truly terrible was happening. Thoughts of her father's experiment surfaced again and again in her memory. It couldn't possibly be a coincidence. Her father had been worrying constantly about this day for some time, and now that that day had come around, a terrible evacuation alarm was sounding.

Finally, Alyx's teacher had managed to get all the frightened classmates into an orderly, single-file line. She opened the door and lead the way out of the classroom and through the corridors of the school. Alyx could see other, older classes leaving their classrooms too. The children in them looked no calmer than those in her own.

Soon, every class was gathered at the front door of the school, the place where Alyx had said goodbye to her mother that morning. Like in many of the areas of Black Mesa, this place was broad and open. Alyx could see across the tiled space, past the transit system's rail, to another platform where there were many panicked scientists and security guards, running this way and that like so many confused ants.

Was her father behaving in the same way? What was he doing now that the alarm sounded? Was he looking for her? Alyx wished she had stayed home that day. She wished the three of them had. She wanted to be with her parents.

The principal of Black Mesa's little elementary school was speaking now. She was telling the children that they would follow the evacuation procedure and take several flights of stairs up to the surface, where they would wait for further instructions from the administrator.

Alyx's mind was elsewhere. If her father's experiment truly was connected to the alarm and evacuation, then he must be in the most danger. He might even be trapped in Anomalous Materials. Alyx's mother would probably be evacuated like every other civilian at Black Mesa, but if Eli was at the source of whatever had got wrong then perhaps he wouldn't be able to leave.

Alyx's classmates began to drift in the direction the teachers were ushering them. Alyx noticed the sound of the principal and her teacher whispering urgently. They clearly had no idea what had caused the alarms, but she did. Just as the teachers turned their backs on her to deal with a crying child, Alyx seized her chance and slipped away. It was possible the teachers would quickly realise she had disappeared, so Alyx made sure she was far away from the group before they started looking for her.

She was in luck. There was a tram waiting for her at the stop. This was the same tram that took her mother back to the dormitories. If she was fortunate she could find Azian and the two of them could take another tram to Anomalous Materials to find Eli.

Alyx had never used the transit system alone before. Her father always told her that she was too young, but that she would be able to soon. Now necessity urged her on. Stepping onto the steel structure, the sliding door closed behind her. Alyx pressed the same button she always saw her mother press whenever she was collected from school and brought home.

The baleful alarms hadn't stopped, and they continued to terrify Alyx to her core. Nonetheless, the usual announcer spoke over the noise:

Good morning and welcome to the Black Mesa Transit System. This automated train is provided for the security and convenience of the Black Mesa Research Facility personnel…

The sound was utterly incongruous.

Alyx still wished to remain unseen, so she neither stood nor sat, but crouched below the steel boundary where no one could see her, though a passing scientist might wonder why a tram was moving without any passengers.

Now and then, Alyx would look over the boundary and peep around, just to make sure she was still going the right way. At one point she noticed another tram moving parallel to hers in the opposite direction. It contained only one figure. A man in a dark blue suit, carrying a briefcase. He had pale skin. Ordinarily, Alyx would have ducked her head down as quickly as possible to remain inconspicuous, but something about this man-made her gaze linger. He was looking right at her. Something about him made Alyx think that he was no ordinary employee of Black Mesa, and he wasn't about to warn one of the scientists about a small child riding a tram all alone in the middle of an emergency. All he did was gaze at her. Alyx couldn't have said what colour his eyes were, but from this distance, they did seem luminous. They stood out against his grey skin. The man adjusted his tie, and in a moment the two trams had passed each other.

If not for the braying alarms, the rest of the transit system's ride would have passed in silence. The tram stopped at the dormitories and Alyx got off.

Like much of the facility designed for civilian use, the dormitories were orderly and habitable. There were neatly trimmed bushes, benches and even a small fountain. Surrounding this central area were the doors to spacious apartments. The Vances lived in number 145. Alyx expected to be able to ask someone if her mother was at home, or even to run into her mother then and there, but the central area was completely deserted. All of a sudden, the alarms gave out and it became eerily quiet. Alyx's footsteps echoed on smooth tiles.

Had everybody already been evacuated?

Alyx wondered whether her mother had gone in some other direction towards the school in order to find her, or else she had been forced to evacuate along with everyone else in the dormitories, hoping that she would be reunited with her daughter sometime later. Alyx knew her mother might not have had a choice in the matter, but nonetheless, she felt abandoned. Just to be certain, Alyx decided to check number 145. She skirted around a bench and passed up one flight of steps. On the second floor, every door was closed and undoubtedly locked. Coming to 145, Alyx tried the handle. It held fast. She was about to turn and go back the way she had come but noticed that the door to apartment 146 was slightly ajar. Perhaps some adult had stayed behind, or else in their haste to leave they had forgotten to lock up. If there was someone there, then he or she would probably know which way her mother had been evacuated.

Alyx gently pushed the door forward. The space was dark, the lights switched off, the curtains drawn. The layout of the apartment was exactly the same as her home. That gave Alyx a little comfort, though she was still apprehensive. As she inched closer into the front hall she thought she heard a scuffling sound from further in. That made her heart lift. There was somebody here.

She moved more quickly but quietly into the space, towards the sitting room. The sound grew louder, and gradually she began to realise that the sound wasn't scuffling, but a low crunching sound, as if something was being eaten.

She had passed into the sitting room now. The space was lit in light blue by the static from the TV, though the sight of the TV itself was blocked by a large armchair, much like the one in the Vance's apartment. This was where the crunching was coming from.

'Hello?' called out Alyx. 'Is somebody there?'

There was no answer, and the grinding, chewing sound did not stop.

Alyx, her heart in her mouth, began to circle around the armchair. What she saw when she was standing to the right of the chair made her blood run cold. At first, she thought her first instinct had been right. It was a person. She could see their arms. They hung limply on the arms of the chair. The figure was slouched in their seat, their legs splayed. But the likeness to an ordinary human ended there. The person's thin shirt was drenched with blood, all of it cascading down from their neck, seeming to originate from the head.

The head. The head was gone.

It had been replaced with a jerking, lurching creature, the like of which Alyx had never seen. She couldn't even have said what it looked like. The top of it was fleshy, smooth and pallid, and two forelegs dangled down in front of it. It must have had a mouth on its underside because it seemed to be using it to chew up whatever remained of its host's head. More blood spurted down from the body's skull, soaking the front of its clothes and the seat of the armchair.

Alyx retched loudly, then began to back away fearfully.

The blood-soaked creature seemed to sense her presence for the first time. The crunching stopped and the fleshy head jerked to the side. Alyx couldn't see its eyes or ears, but it seemed to know she was there.

Alyx turned to run, but the urge to vomit hadn't left her. Rushing to the sink, she voided her stomach into it, then made for the door. Just as she reached it, she glanced quickly back. The monster had risen from its seat. It was several feet taller than her. Its thin shirt had parted, revealing a sickening gash from the groin to the collarbone. Alyx could see the creature's ribs and internal organs. If Alyx's stomach weren't already devoid of its contents she would have disgorged herself again. She darted from the apartment.

By now tears were in her eyes. She wanted her parents. She wanted to wake up from whatever nightmare she had stepped into. Her young mind could barely process the sight of the horrific monster she had just seen.

Alyx quickly sought out the most secluded place she could find: a dumpster at the far end of the dormitories. She pressed her little body up against it. Nothing would find her here, she was sure. Once her heart rate had slowed and she had reassured herself that she was safe here, she allowed herself to cry in huge racking sobs of fear.