The saga sounds pretty cool.
The players' location could be simultaneously raided by two different viking groups, one aligned with Aesir and the other with the giants, that end up fighting among themselves.
Or, more probably, by a single group in which the leadership is being contested by captains aligned with either side. During the raid one surreptitiously tries to kill the other, but instead ends up leaving him knocked out and heavily wounded. The vikings also steal or kidnap something/someone important to the players, and their only trace is the half-dead viking.