From the Introduction:
In this adventure the player characters follow a rumor about the whereabouts of the missing Darkskye Diamond to the Blood Wood, where a clan of kobolds were seen with it. Events transpire that see the adventurers teleported to the dungeon isle of Omen, where they must track down the kobolds to a volcanic lair and stop them using the diamond to resurrect five powerful red dragons. Kobolds feature prominently in this adventure, and it spotlights the varied and often deadly kobolds of 13th Age.
What level characters should I tell players to use?
Omen Quest is an adventure designed to take characters from level 2 to level 4. At the end of the first session the characters level up from 2nd to 3rd level, at the end of the second session the characters level up to 4th level. Two adventures is quite a quick leveling up for characters. In the ongoing story of Tales of the 13th Age it fills the gap between the end of the 2nd level season and the start of the 4th level season. If you decide to play this adventure as a straight single-level adventure then use 3rd level characters.
How does this adventure tie into other adventures?
The Darkskye Diamond was stolen by player characters in Shadow Port Shuffle, and was the ultimate cause of all the events of Wyrd of the Wild Wood, as well as impacting some of the events in Quest in the Cathedral. While it doesn't feature in Crown of the Lich King, it was created by the Wizard King before his fall. Characters who have taken part in any previous adventure have good reason to seek the diamond. If that isn’t a good enough reason it is a huge diamond, and the Dragon Empire would pay to have it back (and others would pay to keep it out of the Emperor’s hands).
At the end of the adventure the adventurers will find a teleportation circle that will teleport them away from the increasingly dangerous kobold lair, possibly leading to the next adventure in this series if the player so chooses to narrate it as so at the closing montage.