One day, Odin and Loki were on a trip in the mountains with no food. They found a herd of oxen and went to cook and eat it.
They attempted to cook the ox but a giant eagle who was actually the giant Thiazi in disguise had done something to prevent the fire from cooking their food. He said he would let the fire cook the ox if he could get his fill.
The "eagle" was very greedy and continued to eat the ox not leaving any for Odin and Loki. This made Loki mad and he tried to stab the eagle. In relatiation, the eagle picked him up and drug him over the mountains. The only way he would let him go was if Loki lured the goddess Idun and her golden apples of youth into the forest.
Loki tricked Idun into going into the forest with him and taking her apples. Not long into their walk the "eagle" swooped down and took both Idun and her apples causing the gods to grow old. Loki tells all the gods he will save her but he needs a disguise so he takes a Falcon suit to get her.
Loki finds Idun imprisoned in Thrymheim. He casts a spell on her to turn her into a nut so he can carry her and escape Thiazi. While flying back to Asgard Thiazi flys after him knowing that he has Idun.
Loki flys into Asgard where the gods are building a wall of wood. Right before Thiazi could fly in they set the wall on fire and Thiazi as well. In the end, Idun, her magical apples and the eternal youth of all the gods and goddesses were saved.