Infiltration into Odin's Vault

: "The Jotuns must pay for what they've done.""They have paid. With their lives. The Destroyer did its work, the Casket is safe, and all is well.""All is well? They broke into the weapons vault."
: ―Thor and Odin
The Infiltration into Odin's Vault was a failed attempt by the Frost Giants of Jotunheim to steal the Casket of Ancient Winters, their source of power, from Odin's Vault in the Royal Palace of Valaskjalf in Asgard. It took place during the coronation of Thor.
Loki, the son of Odin, desired to become king of Asgard and prove himself to his father after years of living in Thor's shadow. As part of this plan, he allowed a team of Frost Giants to enter Odin's Vault. Three Frost Giants killed the guards of the vault and acquired the Casket. However, the Destroyer, defender of the vault, was released from its cell and killed the three. Several other Frost Giants who were still in the process of entering the vault were killed as well.
Following the attack, Thor went against his father's orders and assembled a team of his friends and allies to attack the Frost Giants' home of Jotunheim, demanding answers. This would lead to Thor being banished from Earth, allowing Loki to briefly seize the throne of Asgard before his brother returned.
== Background ==
: "You're the one who showed us the way into Asgard.""That was just a bit of fun, really. To ruin my brother's big day. And to protect the realm from his idiotic rule for a while longer."
: ―Laufey and Loki
Odin, the king of Asgard, united the Nine Realms to establish peace amongst them. In 965, however, the Frost Giants of Jotunheim tried to use the Casket of Ancient Winters to conquer one of the realms, Midgard. Odin and the Asgardians defeated the Jotuns and attacked Jotunheim. Following the battle, Odin retrieved two things from Jotunheim: the Casket, which would be stored in Odin's Vault, and a small Frost Giant infant, the son of Laufey, leader of the Jotuns. Odin left Jotunheim, and the Frost Giants were forced into a truce with Asgard.
Odin raised Laufey's son, Loki, as his own alongside his biological son, Thor. Both Thor and Loki knew that only one of them would inherit the throne of Asgard after Odin. This led to a rivalry being formed between the two sons, however Loki was always eclipsed by Thor, living in his shadow. Loki grew resentful of his brother and, desperate to prove himself to his father, orchestrated a plan to gain control of Asgard. As part of this plan, he anonymously assisted a group of Frost Giants in infiltrating Odin's Vault to steal the Casket. Unbeknownst to the Jotuns, however, was that the Destroyer was guarding the vault and would easily defeat them as they attacked.
== Infiltration ==
: "This was an act of war!""It was the act of but a few, doomed to fail.""Look how far they got!""We will find the breach in our defenses and it will be sealed."
: ―Thor and Odin
In 2023, Thor was about to be crowned the king of Asgard in the castle's hall. As the coronation happened, the Frost Giants began their attack. Due to the coronation's priority, the vault was not as heavily guarded as usual, allowing the Frost Giants to invade easier. As they entered through the vault's small pools of water, the water and ground around it froze to ice. As one Einherjar investigated the freezing, a Frost Giant attacked him from behind, snapping his neck.
As this happened, Odin and Thor sensed the Jotuns' presence on Asgard. The coronation was called off as they and Loki raced to the vault. Meanwhile, three Jotuns would march through the vault and steal the Casket of Ancient Winters. However, before they could escape, the enchanted gate in front of the Destroyer disappeared, and it shot a beam of energy that destroyed the Jotuns, ending their attack.
== Aftermath ==
: "I think you're right. About the Frost Giants, about Laufey, about everything. If they found a way to penetrate Asgard's defenses once, who's to say they won't try again? Next time with an army."
: ―Loki to Thor
Odin and his sons entered the vault, the Destroyer having already returned to its cage. Thor and Odin argued over the attack; while Odin thought it was merely the work of a band of zealots and that it was of little concern, Thor believed it was a declaration of war on behalf of the Jotuns and that they should pay for their actions. Odin asked Thor what he would do, and Thor said he would storm into Jotunheim and break their spirits so that they would not dare to attack again. Odin told Thor he was thinking only as a warrior rather than a king. The two lashed out at each other, and Odin left shortly after.
Loki, though he orchestrated the attack, sympathized with Thor, believing that there was no way of knowing the Jotuns would not attack again. Thor was inspired to put together a team of his friends, comprising of Loki, Lady Sif, and the Warriors Three, to attack Jotunheim, demanding answers as to why they attacked. Despite Loki's apprehensiveness, the team entered Jotunheim, resulting in a battle that only ended when Odin himself arrived to bring Thor and his team back to Asgard. As punishment for his recklessness, Odin banished Thor from Asgard, sending him to Midgard through the Bifrost. He also cast Thor's hammer, Mjølnir, to Midgard, adding an enchantment that "whosoever holds this hammer, if he be worthy, shall possess the power of Thor".