A/N: Hello again! This is the final installment of my Secret Sisterhood Trilogy, but like I said, it can also be read as a standalone. Also, it's my personal favorite one for mainly two reasons: Firstly, I'm still bitter Agent Carter got canceled. Secondly, I really wanted Sigyn to be a part of the MCU, but I also wanted her to be more than just "Loki's faithful wife." I'm still not sure if I should tag her as an OC or not. She is certainly based on her Norse mythology and comics counterpart, but I also took a lot of liberties to develop her character and to fit her into the MCU canon. So, this is how I came up with this "Asgard meets Agent Carter" idea.

On a side note, Sigyn is still Loki's wife here, yes, but this is a very plot-heavy story, not slow burn romance or anything. The first three chapters are to explain Sigyn's Asgardian background, and the rest of the story focuses on her life on Earth, and then the fight against Thanos.

All warfare is based on deception.

—Sun Tzu

As the Queen of the Nine Realms, Frigga was accustomed to the horrors, destruction, and more importantly, the unpredictability of wars. She could never know how her king would return from one. This time, for example, he had returned with a missing eye. And a baby. Laufey's son, he had said. Frigga didn't understand what kind of monster would leave an innocent baby to die on a frozen rock. Surely, even a Frost Giant couldn't be so heartless…

"What exactly do you want me to do, Odin?" she asked softly, while Odin was busy examining his new eye patch in the mirror. It was going to take some time for him to get used to it.

"I want you to be a mother to her."

"That's not what I'm talking about." She knew there was more. With Odin, there was always more.

"Laufey and I have a truce, but I don't know for how long he will remain true to his word. This child, on the other hand, can help us unite Asgard and Jotunheim one day. Bring a true, permanent peace. But until then, no one can know the truth. No one. Will you make that happen, my queen?"

She looked at her firstborn, Thor, who was peacefully sleeping in his crib. He was usually such a loud, demanding baby that it was a rare moment to see him like this. She recalled how excited the people of Asgard had been when it had been announced that their queen was bearing an heir to the throne. If they were going to raise Laufey's son as their own, she had to cast a very powerful memory spell, to make everyone believe that the queen had been expecting a second child, so that no one would question his parentage.

Yes, she could do it, of course. She had cast a very similar spell once before, to make the Nine Realms forget about the horrors Odin's firstborn, Hela, had brought upon them. Among many talented sorcerers and sorceresses, Odin had chosen her for this duty, and that was how they had met. Odin was a young man, then, full of shame and regret. It had broken Frigga's heart, and she had devoted herself to heal his soul after the deed was done. Soon, they had fallen in love and married. After having to imprison his own daughter, Odin had dreaded the idea of siring another child for a very long time, but a king needed heirs. And Frigga was never going to let her sons become like Hela.

"What are we going to call him?"

He thought for a moment, then said, "Loki."

"Loki," she repeated, and took him into her arms. Loki smiled at her. He was such an amiable baby; he smiled at everyone he saw. "I think he likes his name."

Odin approached them and put a kiss on the top of Loki's head. "He is so beautiful. They both are."

"Of course. They are our sons."

He sighed thoughtfully.

"What is it, Odin?"

"There is… something else."

Frigga put Loki into a crib next to Thor's, then held her husband's hands. "Tell me."

"It is Tyr…"

"Tyr?" Tyr was a great warrior, one of Odin's most trusted generals, and a good friend to the royal family. She wondered what was wrong with him.

"As you know, the war started when the Jotuns attacked Midgard. When we were there, Tyr met a mortal woman. A shieldmaiden who was bravely defending her village against the Frost Giants."

He didn't have to say anything else. Frigga had understood. "He is in love…"

"He wants to bring her here and marry her. I don't know what to do, Frigga."

"Does she have a family? Anyone who will want to know where she has gone?"

"Heimdall says her entire family died in the war. The rest of her village will assume she must have died of her wounds as well."

It wasn't an easy decision to make. The mortals didn't belong in Asgard. But if they refused, Tyr might never forgive them. He would continue to serve them, of course. No one would doubt his loyalty. But he deserved to be happy. Ten years ago, he had lost his wife at childbirth. Thankfully, his daughter had survived, but it was still a tragedy.

"I am more concerned about that little girl, Sif. Even if she accepts this mortal woman as her mother, it will last less than a century… Poor thing."

"So, do you agree that I cannot allow it?"

"No, Odin. General Tyr has served you loyally for a long time. And perhaps for the first time in his life, he wants something for himself. You have already lost an eye. Don't lose your dearest friend as well."

…

Frigga cast the memory spell on the people of the Nine Realms. Now they all believed Queen Frigga had given birth to a son while Odin was fighting the Frost Giants in Jotunheim. Midgard was the only exception. While Loki's "birth" was a fact in the other eight realms, it would only be remembered as yet another myth by mortals. Odin believed they were still too primitive to know the truth. "Let them think they are alone in the universe," he would say. And maybe he was right. Every time someone from the other eight realms visited Midgard, mortals started to worship them as gods.

But Odin had let General Tyr bring his beloved mortal, Helga, to Asgard. It was easy to see why he had fallen for this mortal. She was a great beauty, with golden hair, haunting blue eyes, and flawless fair skin. And although she was the weakest being here in Asgard now, no doubt she had been considered a fierce warrior among her own people. Soon, they married under Odin's—and almost everyone else's, to be honest—disapproving gaze. Frigga, on the other hand, saw no harm in this at first. Tyr knew Helga was a mortal. He knew he would lose her after a few decades of happiness. He had explained the situation to his daughter as best as he could. Frigga had helped him as well, and the young Sif seemed to have understood. In fact, she had been most eager to meet Helga. Though she obviously saw this mortal woman as a pleasant oddity, rather than a mother figure. But then, perhaps that was for the best. As for Frigga, she actually admired this mortal's courage to leave everything behind and follow the man she loved to a realm of unknown. Perhaps that was why the two had warmed up to each other so quickly.

But five years after the wedding, Frigga started to question the wisdom of this arrangement when Helga came to her one morning, and told her that she might be with child.

"Are you sure?" Frigga asked.

"No, but I haven't bled in two months, my queen. I didn't know who else to go. Please, help me."

She was right to be anxious. A half-mortal, half-Asgardian child… Such a being had never existed before. Not to Frigga's knowledge, at least, and Frigga considered herself quite well-versed in the history of the Nine Realms. Still, she pitied this woman. Mortal lives were fleeting; it wasn't fair that they had to live their short lives with such burdens.

She took Helga's arm. "Come, let's see Eir. She can tell us if you are really with child."

On their way to the healing room, they saw Thor and Loki, playing in the gardens.

"Mother!" Thor cried, running towards her with a small snake in his hand. "Look what we found in the gardens! Isn't he beautiful?"

"He is, indeed. But please put the poor creature back where you found him."

"Yes, mother."

"Where are you going?" Loki asked.

Frigga decided not to lie to him. "To the healing room."

"Is Lady Helga ill?"

"She's a mortal, Loki. Why are you so surprised?" Thor said, but bit his lips when he realized how his mother was staring at him. Frigga knew he had meant no offense, but Thor could be so brusque sometimes. "Apologies, my lady, I didn't mean… I'm sure you're as healthy as a Bilgesnipe!"

Well, it wasn't the most graceful apology, but at least he had tried. It had made even Helga smile. Frigga kissed his sons, and told them to go back to playing.

When Eir, the most talented healer of Asgard, heard that Helga might be pregnant, she obviously did her best to keep an indifferent face, but Frigga knew her well enough to see how troubled she had become. Nevertheless, she told Helga to lie on the table, and ignited the Soul Forge.

A few moments later, she confirmed that Helga was indeed with child. And it was a girl. The mortal woman was smiling when she sat up on the table, but there was fear in her eyes.

"Tell me the truth, Eir. Will my daughter be like… you? Or me?"

Eir sighed thoughtfully. "It is hard to say. You must understand, Helga, you are the first mortal who was allowed to marry an Asgardian. Were you and General Tyr hoping to…"

She blushed in embarrassment. "No. We didn't even think it was possible."

"Well, your child is certainly going to be… unique. Whether this is a good or bad thing, that is not for me to say. But she is perfectly healthy, for the time being."

Frigga helped her get on her feet. "Come, Helga. Let's go back to the palace. Thank you for your counsel, Eir."

She bowed to Frigga. "My queen."

"Helga," Frigga started as they made their way back to the palace. This wasn't an easy to thing to say, but as a queen, it was her duty. "Like every woman, you deserve to experience motherhood. And I have no doubt you would be a great mother. But you heard Eir. Perhaps it would be more merciful if—"

Helga stopped, and put her hands on her belly in a protective manner. "My queen, please! Don't do this to me! Don't kill my unborn child!"

"No one is going to force you to do anything you don't want to do. As the Queen of Asgard, I give you my word," Frigga assured her. "But you and Tyr must think this through. For your daughter's sake."

"We will, of course," she said, but Frigga could see that she had already made up her mind. She was going to give birth to this child, no matter what everyone else said.