The three druids of the Druid Council of Freehaven are secretly worshipers of Malanel, an evil god of silver, the moon, and domination. They've found a way to use Malanel's magic to create silver necklaces which let them command werewolves. They've converted several people into werewolves and then put the necklaces on them to command them.
The druids have werewolfed and mind-controlled Ambassador Niodien at the Summerblossom Embassy, which is how they found out about the Orb of Storms. For the past year, the druids have been stealing all the rainfall using their weather magic. Their plan was to get the Empress to send the Orb of Storms to the valley and then steal it. That plan has succeeded.
The druids' original plan was to spend a few days in town, bonding with the Orb to gain control over the storm, and then take it deeper into the Empire and present it to the Elders. That plan needs some modifications: the Orb wants chaos and vengeance and destruction, and more specifically it wants to call hailstones and tornadoes to wipe out a village, and it won't form any sort of bond with the druids until they let it do that.
So: the druids keep the Orb of Storms in their village Freehaven for two days, and then they take it out in the wilderness and perfom a ritual to let the Orb wreck the elven village of Cedar Valley. If the player characters fail to retrieve the Orb while it's in Freehaven, they get one last chance while the druids are performing the ritual.
Note: This adventure doesn't really discuss the rulership of the Federation, but please assume that the Malanel-and-werewolves thing is widespread throughout the nation.