Hi everyone,

Back with another chapter, which will explain why Catelyn and Sansa were locked up at the very end of the previous chapter.

MARGAERY XXIV

She was in a dark place, a very dark place, but it wasn't a dreadful place like a cell or a dungeon. This one was familiar, home to beautiful moments she shared with her husband. There were torches hanging from pillars, all lit up. The ground under her bare feet was made of sand and rock. Before her was a vast pool, or something that looked like it. It was a great body of water, more than large enough for dozens of people to easily swim in it. She could see stalactites and stalagmites all over and around the pool.

Her shoes laid next to her. She had removed them. She removed her gown, then her smallclothes as well, then unbraided her hair. She felt it fall in curls behind her back and over her shoulders, covering her breasts. The place was warm, and she could feel a soft breeze run all over her skin, tickling between her legs, under the laps of her arms, on the region under her chin, in the space between her ears and her head, between her fingers, between her toes. She slowly walked to the pool, sand and pebbles crunching under her bare feet, until the left one sunk into the dark water. A pleasant chilly sensation reached the extremity of her toes as sand filled the spaces between. The right feet sunk next to the first. She kept going forward, water submerging her ankles, her knees, her thighs, her entire legs, her hips, her tummy… She realized it was bigger than usual. Smiling, she resumed her path, always forward. Her breasts, her arms and hands, her ribs, her shoulders, her neck followed under the water, until only her face emerged. She waved her arms and legs to remain at the surface, then dipped her head into the water.

Water was surrounding her. It was cold, but no different from the water in the rivers and lakes of the Reach. She opened her eyes, and could see nothing. It was complete darkness. Her hair was dandling all around her face. She pushed with her legs and feet and came back to the surface, pushing aside her hair that fell on her eyes. She breathed deeply and laid on her back, letting the water carry her, her eyes closed. The tip of her head hit something hard. It was a column with stalagmites around the base. She swam away, feeling at peace as she travelled from one end of the pool to the other.

She came back on the shore. There were a few towels laid on the ground. She rested her back on them, letting the water roll on her immobile body, covering her eyes with her arm to not let the light of the torches bother her. It was an intimidating place from some perspective, and yet a pleasant one, where she was alone, safe, quiet. You could hear the thunder over your head but you knew you were safe here. She looked again at the dark water, wondering how deep the bottom was. Why not try to find out? There was a natural platform not far away, about four or five meters over the pool. She went there, and jumped from it. Water flew all around her when she hit the surface. She heard it. She sunk deep, without touching the ground. She came back at the surface, took a deep breath, then dived again. She kept going down, deeper and deeper. Finally, her hand touched something. She felt sand as she rubbed the surface, but as she kept tossing the sand away, she realized that under, the surface was smooth, yet solid. She couldn't see anything with the darkness around her. Keeping her breath began to be difficult. She gave herself a good push with her legs on the ground and swam with all the energy she could muster to come back to the surface. She let go the air in her lungs. There was a troubled light ahead. She had to reach it. Her strokes became more desperate. She had to reach the light.

She reached up, and the tip of her fingers brushed the air. One last push, giving away all the air left in her burning lungs, she reached the surface, coughing while she grasped all the air she could. Slowly, she swam to the shore. She laid there, her body up to her tummy still in the water, laying on her side, breathing with difficulty, coughing at every turn. She turned on herself, lying now on her back, her coughs repeating themselves without any way to stop them.

She had spent so many wonderful times in this place. Deep into the mountain, Tyrion had brought her here early in their marriage, when she told him how she used to bath in the Mander, but also in other lakes and rivers with her friends and family. The water of this natural pool was relatively warm, and so was the air, though Margaery felt it was more heated than usual. All the torches made the place seem so illuminated, yet it maintained a certain dark atmosphere that made it all the more mysterious. And as usual when she was with Tyrion, especially in that time, they had made love. Each time they had come together to this place, they made it in the water, on the sand. It became one of their intimate places, only accessible to both of them. Perhaps it had been there that their child was conceived.

She placed her hand on her growing belly, caressing it. She had wanted that child so much. Maybe her reasons were somewhat different today than they were at the beginning of her marriage, but finally they had managed it. And in that very moment, there was nothing in the world Margaery wanted more than to have her husband by her side.

Instead, she remained alone, half her body soaking in the water, her cough not stopping. And she began to get cold. Extremely cold.

As darkness engulfed her, she turned to her side. Instead of her eyes meeting the sand of the ground, she met the barely visible furnishing of her bedroom. No more granular ground under her, only the comfortable featherbed she always slept in. Except this time it didn't feel comfortable at all. She was cold. So cold. Her breathing was ragged, and her head… Gods, how her head hurt! She lied on her back again, eliciting a series of coughs, just like she did in her dream. Or was it a dream? She began to shake as a result of how cold she felt, and she brought back the covers she had pushed aside in her sleep.

But now she felt too hot. She was sweating, her head was spinning, and when she brought her hand to her forehead, she felt it burning. Her breathing itself, when she wasn't coughing, was hard. She couldn't help but moan in pain. Slowly, she removed the covers, immediately regretting it as she froze, but she resisted the temptation to cover herself again, rolled to her side and, slowly, sat on the side of her bed and stood up. She closed her eyes, wincing in pain from her head. She shivered, instinctively hugging herself to bring a little heat to her body. Slowly, she advanced, but her head kept spinning and all went black.

When she regained consciousness, she was lying on the floor, her back to the ceiling. The cold surface made it worse for her. Despite her desire to do so, she felt so weak, she couldn't manage to stand back on her feet, and she remained there, quivering, coughing again, and again, and again.

Slowly, so slowly light crept into the room. Margaery tried to creep as well to her door, but even that she couldn't do. It was as if her members and her whole body had become so heavy she couldn't move them by the smallest inch. And so she remained there, waiting, unable to move, unable to sleep, unable to rest, unable to do anything. It was as if her body parts were filled with melted lead.

Dawn arrived, and not long after, the door opened. Margaery made an effort that felt superhuman for her to look up, which led to several more coughs from her throat. She dropped her head, her forehead meeting the cold floor in what felt like a powerful impact. She felt as if her head was about to blow.

"Lady Margaery."

She recognized Sera's voice, though it seemed as if it was coming from another world. Margaery didn't even feel strong enough to look at her handmaiden. She heard the sound of something being dropped, then footsteps. Then someone gripped her shoulders and forced her to look up.

"My lady, are you alright?"

"Ser…" Her attempt to say the name of her handmaiden ended in a long succession of uncontrollable coughs. Her throat was burning. She caught a glimpse of Sera's horrified expression.

"By the Seven!" Margaery barely heard what she said through her coughing, but next she clearly heard Sera call for the maester. "My lady, you must not stay here on the floor."

Sera began to make her stand. All the while, Margaery kept coughing. Sera placed an arm around Margaery's shoulder to support her as they walked. Margaery opened her eyes. Her vision was blurred. The world was turning around her. And then she vomited. She lost the support of Sera's arms and fell. Her head came to contact with a viscous liquid, and some more left her mouth.

She felt a pair of arms seizing her again, then laying her on her back upon a more comfortable surface. Something was about to come out, but it didn't. Margaery's coughing got even worse, as if whatever didn't leave her mouth now blocked it. Someone, probably Sera, wiped what of her vomit had been left on her face. All the while, Sera's voice kept calling for her, but Margaery simply had no force left to open her eyes. Turning her body to be on her side, her world went spinning, even under the complete darkness of her closed eyes.

She had vague notions of events happening around her. Sera still calling for her, but stopping after a while, a wet cloth being placed on her face, more footsteps, a man's voice, whispers around her, someone saying it's the same. And people moved her, manipulated her like a doll, making her lie on her back again, then placing her in an almost sitting position with pillows supporting her. All the while, she could barely move, and the few times she opened the eyes, she could barely distinguish what was going on around her. And the coughing, coming again, and again, and again. The dampness of her forehead, the sweating of her whole body as covers were brought all over her, the excruciating pain in her head, the burning in her chest, the pain she felt every time she moved anything even by an inch, no matter the part.

She was in the water, but could not recognize the place where she was. All around her, a brown river. She could see the shores both to her left and right, but all they showed was sand. She started to swim in the direction of the closest shore. Salty water entered her mouth, which she spewed back. She could not see the floor of the river. Salt irritated her eyes. She did not seem to get any closer to her destination. And then, the brown water started taking another color. And soon, she realized it was red, and she tasted blood on her tongue. She turned away, only to realize the water behind her had turned red too. She tried to remain on the surface, but her arms couldn't maintain her, the blood slipping through her fingers. Soon she was engulfed, and she fell into a lake of death, never to arise again.

Next she was in a familiar place that she didn't recognize right away, but soon realized it was the Great Sept of Baelor, and that she wasn't the only one to be there. People were gathered in two groups, face to face, in such a way that a free path was left from the entrance to the altar. Someone dressed like the High Septon was waiting by the altar. In front of her, Margaery noticed the Grand Maester Pycelle, the Master of Whisperers Varys, Cersei and an old man she never met, but who she recognized right away. She balled her hands, wanting to cross the free path and strangle Tywin Lannister with her own hands, but she couldn't move. Here they were, right there, two people she hated, two people who hurt those she loved the most and there was nothing she could do. She tried to speak, but it was as if her tongue was glued.

A cough behind her caught her attention. Turning around, she realized that her grandmother, her parents and her handmaidens were all there… along with Loras. She couldn't believe her own eyes. She tried to reach for him, to say something, but again was stopped from doing so. He was so close, and yet so far away from her.

A loud noise announced the opening of the large doors of the Great Sept. The outline of a figure appeared in the light of day, and as Margaery's eyes adjusted and the figure approached, she realized it was Sansa. She wore a golden dress and her hair was braided in a way Margaery had never seen on her. And then another person Margaery hated approached her. It was Joffrey.

"What are you doing?" Sansa asked him.

"Your father's gone. As the father of the realm, it is my duty to give you away to your husband."

He extended an arm, and Sansa begrudgingly took it as they both began to climb down the steps and the heavy doors closed behind them. Margaery wanted to do something, to stop it. Sansa had already suffered more than enough, but again, like always, she was stuck into place, unable to speak.

As Sansa approached, Margaery noticed the symbols on her dress, a mixture of a wolf and a fish at the bottom and lions on the top. And then her eyes got caught by Joffrey's, who looked at her with that evil grin she saw too often. Then darkness surrounded her again.

Next she was in a dark cell, climbing on a chest to look through the window. In the courtyard of an unknown castle, she witnessed her brother Loras being brought to an execution block at the cheers of a crowd. She watched, helpless, as he was forced on his knees, his neck on the block, then as an axe cut his head from the rest of his body. Again, she tried to scream, but nothing came out of her mouth, her despair contained inside her motionless body.

Then Margaery got back the use of her body, only to be surrounded by green flames all around her. She tried to find a way out of there, but there was no way out to be found as she suffocated, coughing out everything her belly contained, falling to the ground as the heat engulfed and consumed her entirely.

There were people shouting all around her as she kept coughing and vomiting bile, her face covered with sweat, her clothes glued to her body, her hands and feet held together by strangers as a pain like she never experienced before travelled through her entire body.

Then she was back in another dark place, but this time stars were looking at her from the ceiling. Turning her head around, she noticed strange walls and other structures around, some emitting a light she never saw before despite the darkness surrounding her. And then, looking up again, she saw a blue shape, a person without hair, grey-eyed, looking back at her.

Then she walked down a dark corridor, with dead bodies lying all around, following a woman wearing only black with a bow and arrows on her back. Then they emerged in a strange room with people lying all around as well, but this time who moved and spoke, sometimes missing an arm or a leg when it wasn't both. People who were injured. The woman who walked with her stopped and turned to face Margaery. She was about the same age as Margaery was, with black hair brought into a single long braid. She said something unintelligible, about being unable to help someone.

"Just let them see your face," Margaery replied, without knowing why.

And then the world was burning again, with deafening noises all around. She ran away from the flames of death the best she could, barely noticing a fire arrow touching a large object in the air. This object fell very close to her and Margaery ran in the other direction, until a large burst of fire engulfed her.

Again, she was deep into the pool of the watery cavern. She was trying to swim up, to get back to the surface, but a force seemed to bring her back to the depths of this world. She was drowning, and no one came to her help.

Then she was pushed forward and ended up in a pool of mud. All around her deafening noise made her head ring in such a way that she screamed, but couldn't hear herself among this cacophony. She raised her head, barely able to see through the mud, but distinguished burst of earth and dust rising all around. And men running all around, some ending up flying in the air or disappearing in one of those burst of earth. They had strange helmets, and strange swords which they pointed forward despite being no enemy standing in front of them. And then there was another man, this one wielding no sword but only a shield, running faster than the others, taller than the others. Margaery only got a glimpse of his shield, barely seeing the silver star at the center and the red, blue and white rings around it. Then she was engulfed in another burst and her head spinned so much she vomited again.

And the stood in the light. Complete light, as it was. And she heard voices around her.

"Everything is going to be fine, sister."

She recognized this voice. "Loras!"

"Everything is going to be fine, my little rose."

My little rose. It had been so long since she was called this way. It was a nickname her mother gave her when she was very little. Sometimes, she could remember the time when everyone she loved, her mother, her father, her grandmother, her friends, even Loras called her this way.

And then light was gone, and she was back in darkness. Then she was back in the blood sea. Then drowning. Then the sharp light came again, causing more headaches. And then fire surrounded her again, before being replaced by darkness, then by the water, then by a complete void. She moved from place to place, freezing then burning, drowning then suffocating, her head split by deafening sounds then surrounded by complete silence, feeling excruciating pains then nothing, screaming and crying then lifeless, back in her room then out, seeing while unable to look, hearing while unable to listen, feeling sharp pain yet unable to voice her suffering.

People visited her. All sorts of people, dead and living. Her mother came to remind her of the duties of a wife and mother. Her grandmother reminded her men, even clever men, were stupid at the end of the day. Genna told her how she thought Casterly Rock should be ruled in her nephew's absence. Joffrey just came to sneer and to tell her he was the king. Sansa wondered if Margaery was feeling well, though Margaery knew she more than anything wanted to know when she would be reunited with her family. Robb Stark asked her conditions against peace with the North. Ser Jaime told her how he loved his brother. Loras boasted about his latest conquest and victory in tournament. Cersei Lannister wondered if Margaery's weak physical condition could explain her attraction to her brother. Ser Kevan presented his respects. Tommen asked her for advice about how to be king. Ser Barristan wished her the best. Her father told her how heartbroken her mother was by Loras's death. Sera asked her what she wanted for dinner. Mira asked what she would wear today. Willas said how eager he was to marry Mira.

Even the father-in-law she luckily never met came to visit her. He just stared at her as he stood tall next to her. And then, like by magic, she could talk.

"Why did you do this?"

"Because he's a Lannister."

His answer echoed all around, making Margaery's head spin once more.

And then Tyrion was there, holding her hand. She gripped it, not wanting to let him go, and looked straight into his eyes. She said nothing. They didn't need any word to let each other know how they felt. But his hand slipped, and his face faded.

And then she opened her eyes to the dim lights of candles. There were three, supported by a candlestick far before her. Most of the wax had already melted. Maybe a quarter was left of it. The fire remained still most of the time, though it wavered from time to time, leaving Margaery wondering if it would vanish.

She was hot. Her breathing was ragged. She tried to move her leg, only to feel the cover glued to her. She coughed slightly, weakly, closing her eyes again. Then she heard movement next to her, something dripping, then a wet cloth was pressed against her forehead. She moaned and turned her head, the cracked open her eyelids, meeting a familiar pair of green eyes on a pale face.

"Mira?"

The movement of the cloth stopped. The woman Margaery just addressed blinked. "Lady Margaery? You're awaken?" she whispered.

Margaery tried to answer, but her words remained stuck in her throat. She made several attempts before uttering a few words. "Wha… What's going on with me?"

"You're sick, my lady. Very sick. You've been unconscious most of the time over the past few days."

"I…" Margaery struggled to make the words come out of her mouth. "Where is Tyrion?"

"Lord Tyrion is in the Vale with the army. We received word from him recently. He's fine. Look, my lady. You must rest. Maester Creylen says you've gone through the worst, but you'll need time to recover. Please, don't tire yourself. Try to sleep."

Margaery tried to say something else, but all she could utter were mere syllables as she was driven back into darkness, too weak.

The following days continued in the same way, shared between endless dreams and short moments of consciousness. When she was conscious, Margaery could barely drink something and get a bite or two. She still could not sit in her own bed, and she couldn't remain awaken more than a few minutes at the same time. Creylen came to visit her regularly, according to Mira, though she was never awaken when he did. Her friend always remained at her side, taking care of her. She was the only person Margaery saw.

One day that Margaery felt a little better and she had more energy, she finally asked.

"Mira, what's going on really?"

Her handmaiden had been doing some lecture for her. She begrudgingly set aside her book and looked straight into Margaery's eyes.

"There's been an outburst of plague in Lannisport, and it reached Casterly Rock. First, there were only a few people who got it. No one really noticed anything was amiss. Then you got sick as well, and so did other people. The gates of Lannisport were closed, and so were those of Casterly Rock, and all the sick people were confined to their chambers. But the sickness continued to progress."

"How come I wasn't informed? There were people who got sick. I should have been told."

"At first, there were only servants, so no one really noticed it. According to Creylen, this is only a cold, but a very strong cold. People start to feel weak and tired, along with some muscular pain, and then after a day or two they are burning with high fever, experience headaches, a fatigue so extreme that they're not capable of moving, and many cough and vomit. People often lose consciousness, only for one day most of the time, though in certain cases they remain unconscious for days. And then they start to recover. Or they die. When they get past the worst part, they recover. I know because I did."

Margaery widened as much as they could. "Mira, you got it?"

She nodded. "That's why I left early on an evening and I didn't come to work the day after. I tried to crawl out of my bed, but I just ended up on the floor of my chambers. And… I emptied whatever I had in my stomach."

Margaery smiled at the irony of Mira's reluctance to admit what she did. "The same happened to me. Sera found me in this position."

"Yes, she told me. She was really worried about you. We all were."

Margaery looked at her friend. When she regained consciousness previously, she never gave particular attention to how Mira looked like. Now, however, she noticed that she looked paler than usual.

"Mira, how do you feel?"

"I feel fine, my lady."

"Mira", Margaery said on an exasperated tone, making it plain that she didn't believe her.

"I am, my lady. When I started to get better and I was told how ill you were, I asked to stay with you all the time. Maester Creylen wasn't keen with the idea in the first place, but people kept getting sick and since I already had it, he judged I couldn't get ill again. So he allowed me to stay so I could keep an eye on you at all times. I just had to wear a cloak to prevent me from getting cold, or to wrap myself in a blanket sometimes. I'm truly fine."

Margaery decided to give up. "How did that happen? This? Where does it come from? How come we didn't see it coming?"

"Maester Creylen believes it comes from the Iron Islands."

That caught Margaery's attention. "The Iron Islands?"

"He told me that he exchanges letters with many maesters throughout the realm, and a few of them are serving families in the islands. Recently, they informed him of a strange disease that had started to plague the Iron Islands. People had the same symptoms as we have now. He believes we didn't experience this disease before because Balon Greyjoy didn't allow any ship to leave the harbors on his islands."

Margaery struggled to understand all that it meant. And then she realized something. "Our invasion… Our fleet…"

And then her energy was down. She didn't mutter the words, but she thought of the ships of the Lannister fleet that were sent to invade the Iron Islands. Some of them had come back to Lannisport to replenish themselves with weapons and food necessary for the invasion, or brought back the injured soldiers. They had brought this plague back with them.

"Mira…" She could barely pronounce words again. "Why… am I so weak?"

Why didn't she recover as quickly as Mira. Her friend may have looked paler, but she had obviously recovered only after a few days. Margaery didn't. Mira placed a compassionate hand in hers.

"My lady, you just need to rest. You'll recover, you'll see. You'll get through this."

Margaery nodded as sleep gained her, bringing instinctively her hand to her belly and the child who kept growing in it.

When Margaery next woke up, they were in the middle of the night. Some candles still provided a faint light, but Mira was sleeping in a very small bed not far from her. Placed against the wall, this bed must have been brought so Mira could watch over Margaery at all times.

Margaery knew she ought to rest, but she was tired of staying inside the same bed, alone. Slowly, painfully, she sat on her bed. Whether it was from the disease or from the chill of the night, she quickly brought her covers around her. At the end of her bed, a nightgown was laid, probably by Mira. Margaery slowly put her feet on the cold stone, the contact sending a shiver through her whole body, and walked at a very slow pace to the gown that she put. She had missed the feeling of the fabric on her skin.

She went to sit in a chair near the balcony, although the latter had been closed to prevent more fresh air from entering. She remained there, sitting, enjoying not being confined to her bed, while not feeling well at all at some moments.

She must have drifted away for the next time she woke, in the middle of the day, she was back into bed, and Mira was at her side once more.

Margaery could already feel that she was better than the day before.

"Mira."

Right away, her friend put aside the book she was reading. "My lady. How do you feel today?"

"Better, I think." She produced a quick cough, as if her body protested her statement, though her coughs had kept turning smaller and weaker since she emerged. "Mira, I want to know what is going on. How many other people are sick? How many died?"

Mira didn't tell her that people died, but Margaery hardly imagined that such a plague would make no victims. With reluctance, her handmaiden started to tell her the truth.

"From what I've been told, there are victims among servants and soldiers, especially among the older people. And… Ser Emmon Frey, Lanna and Alla died."

Margaery closed her eyes. Lanna Lannister was the wife of Ser Antario Jast and the daughter of Ser Damion Lannister. Both her husband and brother had gone to war, while her father stayed behind. Although Damion was not the person Margaery was the closest to, she felt for him. Worse was the death of Alla, her cousin who had come with her from Highgarden.

"How does Genna feel about her husband's death?"

"I don't know, my lady. Until recently, she ruled the castle while you were… bedridden."

"Until recently?"

"She got the disease as well. She's stuck to her bed right now."

"Who manages the castle, in this case?"

"It's not clear. King Tommen remains confined to his chambers. Everyone is afraid he might get it. I think in some way, Maester Creylen is running the castle. With so many people sick or who lost a loved one, I don't think anybody is really leading."

Margaery shook her head. "That must change."

She began to sit up. Mira grew alarmed right away.

"My lady, you must…"

"Don't tell me that I need rest. There's no time for that. I must take matters into hands before it degenerates. And don't tell me that because I'm carrying a child, I can't perform my duties as lady of this castle and Lady of the Westerlands."

Margaery had said the latter angrily. The conversation she had with Catelyn the evening before she got sick had come back to her mind. She was now sitting in her bed, her feet about to touch the floor, her hand on her belly to emphasize what she just said.

It was then she realized something was amiss.

She stared right into Mira's eyes. Her friend stared back at her, with a look Margaery didn't remember ever seeing in Mira's face. Mira was ashamed.

Slowly, Margaery looked down. First, she closed her eyes, preparing for the inevitable. Then she removed her hand from her unusually flat belly and opened her eyes. The curve was gone.

Desperate, Margaery looked back at her handmaiden. Mira's expression had now turned into one of deep sadness.

"I'm so sorry, my lady."

"Mira…" Margaery heard her voice shivering, though it sounded as if it came from far away. Her friend looked down, avoiding her gaze. Then the fatal words came out of her mouth.

"You had a miscarriage while you were unconscious."

I hope that not too many of you will hate me for what just happened.

In truth, years ago, when I wrote down a plan detailing where this fanfiction would go, I had already decided that Margaery would lose her child. This is a medieval world. Losing a baby at his birth, or mothers dying in childbirth is not rare (we only have to look at Catelyn and Tyrion's mothers). However, the circumstances of Margaery's loss of her child are different than I initially planned. I think COVID-19 made me so depressed and played some role in my blocking recently that I ended up including an epidemic into my fanfiction. Since the Iron Islands were isolated from the rest of the Seven Kingdoms at the beginning of the war, a new disease could have appeared there without much people noticing. The fact very few houses in this region have maesters would furthermore have made the detection of any new disease much harder.

Many of the dreams Margaery made while suffering are inspired by Margaery Tyrell/Natalie Dormer appearances in other Game of Thrones material and various other medias. In order :
- My other fanfiction "A Shadow and a Wolf" (the dream in the watery cavern also appears there)
- "Game of Thrones" TV show (the scene of Tyrion and Sansa's wedding in Season 3)
- "The Tudors" TV show (where Natalie Dormer played Anne Boleyn)
- "Game of Thrones" TV show (Margaery Tyrell's last scene in Season 6)
- "Mass Effect Andromeda" video game (where Natalie Dormer voiced the Asari doctor Lexi T'Perro)
- "The Hunger Games: Mockingjay Part 1" movie (where Natalie Dormer played Cressida)
- "Captain America: The First Avenger" movie (where Natalie Dormer played Private Lorraine)

Please review (and try not to be too hard on the author who had his power couple's baby die).

Next chapter : Davos