From the publisher's website:
You play the Norse Gods and you must repel your Enemies out of Asgard, your world. During your turn, you can perform 3 actions among the 9 at your disposal, each one corresponding to the 9 worlds of Yggdrasil. For instance, you can get weapons from the dwarves, look for vikings’ souls, fight against the enemies or the giants, ask for the help of the elves or the vanir. Moreover, each player has one personal power, which is unique and helps him to play. If the enemies move forward too far in Asgard, the game ends and you all lose. If you stand firm until the end of the enemies deck, you win the game all together.