This is pulled directly from the Gatewalkers adventure path player guide.
Six months ago, a rash of strange paranormal phenomena occurred around the world. Chief among the incidents reported were countless instances of aiudara—elven teleportation portals, also called elf gates—suddenly overflowing with tremendous white light. As aiudara are often located in remote locations, witnesses were relatively rare. But those onlookers who were nearby and who gazed into the light saw : a loved one, a lost homeland, a glorious treasure. The specifics varied in each account, but in every case the witness saw whatever person, place, or thing they most desired. Few could resist the impulse to walk toward the light in the hopes of grasping the apparent object of their obsession. Many never returned. Those who did were forever changed.
The crisp summer evening on which this event occurred became known as the night of the Missing Moment.
Lost Time
No one who walked through an aiudara during the Missing Moment remembers what happened next—their memories of whatever transpired on the other side of the white gate were totally and irretrievably wiped. So far as they’re aware, one moment each traveler was stepping into the door, and the next they were stepping back out, only to discover that they had, in fact, been gone for minutes, hours, or in some cases even days.
In your case, as a player character? You were gone for three months. Many others never returned at all. In time, the individuals who took this journey would come to be called gatewalkers. Though some gatewalkers bore obvious signs of their travails on the other side of the aiudara—unfamiliar scars, for example, or a strange new hue to their hair—others returned with practically nothing to show for their trip, save for one: all returning gatewalkers now bare a similar brand somewhere on their flesh, most often on the back of their neck. This brand, made of thick lines set into the skin like a tattoo, seems to depict a mountaintop archway limned with four stars. This “sign of the gatewalker” quickly became an obvious marker of those touched by the paranormal.
Gatewalkeres
Your character is a gatewalker, as are the other members of your adventuring party. While your individual motivations for stepping through an aiudara that fateful evening undoubtedly differ (as do the strange powers you each manifested afterward), you’ve joined forces in light of your mutual experiences, particularly your unusually long absence.
Your group has assembled under the banner of one Dr. Etward Ritalson—a peculiar Ustalavic researcher and fellow gatewalker determined to understand what exactly happened during the Missing Moment. His funding and leads are your best chance at not only recovering your lost memories, but also of better understanding (and perhaps advancing) your new deviant powers. Dr. Ritalson has explained that his skills and interests are better suited toward the laboratory than the open road, so he’s gathered your group together to conduct field research in his stead.
Dr. Ritalson’s Mission
At the start of this campaign, you and your party members find yourselves in Sevenarches, a heavily forested realm in the River Kingdoms of northeastern Avistan. Dr. Ritalson has led you here to pursue his current best lead into the cause and meaning of the Missing Moment: a strange ailment called the Obnubilate Curse. This centuries-old affliction formerly affected any elves who stepped foot in Sevenarches, but on the night of the Missing Moment, all traces of the curse suddenly abated. Moreover, Sevenarches is the locale of the famed Seven Arches—an array of aiudara which no doubt bear clues regarding the gatewalker mystery. Dr. Ritalson believes that the obnubilate curse and the Seven Arches hold the keys to better understanding the Missing Moment. With you as his agents, your collective is well on its way toward uncovering the answers you all seek.