One day, Thor wakes to find his hammer, Miollnir, missing from it's usual place. In a fit of anger he suspects that Loki took it.
Thor still angry, blames Loki for taking his hammer, and out of confusion for the acusation Loki try's to think of where it might of went.
...The giants... Could have taken the hammer...
Loki, follows through with his plan to try and find Miollnir by flying well above the land and using his hawk vision to locate it. After hours of searching, he gives up, but out of the corner of his eye, he sees the Frost Giant's castle. After talking with the Frost Giant, he returns to Asgard to tell Thor that the Frost Giant has his hammer hidden and he wants Freya for his wife. She declines to be marry him, so Loki comes up with another plan.
Loki's plan was to get Thor to shave his beard, and dress up as Frieya, which worked. After a few minutes of eating and talking, the Frost Giant tells a few servants to bring Miollnir as a wedding gift.
Thor get's up, rips off the disguise and grabs his hammer, striking down the Frost Giant.
In the end, Thor and Loki were victorious, with Miollnir in safe hands.