"With this necklace I can locate you and contact you no matter where on Eberron you may be. I will call on you if there is need. Keep it safe and speak to no one but myself and the masters about any of these events." Matron Marta accepted the adventurers' frozen silence under her stern gaze as confirmation they would follow her instructions. With a quick nod she dismissed herself to return to other duties.
The team of fledgling diggers performed well—better than expected considering the circumstances. Maybe there are some heroes among the bored nobles and disenfranchised mercenaries flooding the union since the Last War ended, thought Marta. It gave her hope to find a resourceful batch of initiates.
A thorny problem remained. Two civilians plus a digger and a Morgrave professor were murdered, an invasion from a mysterious plane narrowly averted, a union patron implicated in the plot, and the sinister mind behind it all was still loose. She worried zealots among the union's political enemies could use these event to their advantage. "'Dol Arrah's Light,' I hope these new recruits have the sense to keep their mouths shut," muttered Marta. The pseudodragon joining her march from the dormitory chirped its agreement.
The trouble started two days ago with the discovery of Delvron Gaunt dead in his room. Alive, Gaunt was vicious and a relentless drunk. Dead, he was even more unsettling. The Cyran veteran crouched in the corner of his littered cell eyes wide open and his face twisted in agony and fear. He had several minor wounds on his back and legs, and had carved his last testament in his own chest with the bone-hilt dagger he still grasped, "Aryth in Tiamat they come." By the time word reached Marta, a team of initiate diggers was already starting an investigation. Viewing it as a chance for them to prove their worth, Marta tasked the team with unraveling the mystery of Guant's death.
A thorough search of the scene turned up some mysterious clues: several spongy stones made of a reflective material, the address to a house in the Castleview District, and the very message carved in Gaunt's chest. Although unusual, the team learned a great deal about each lead using standard investigative techniques. Consulting an expert mirrorwright, they learned the stones were actually some kind of flesh but not from this world. The address belonged to an elderly couple, the Fellons, who owned the Crook Observatory just outside Wroat. Researching the meaning of Gaunt's last written words, they discovered "Aryth in Tiamat they come" referred to a cosmic conjunction of the moon Aryth and the constellation Tiamat approaching its zenith in the next day or two. It was also a quote from Belental Heirm's Deviant Celestia.
In his life's work, Belental Heirm advanced the theory that Eberron's planes' sometimes-erratic movement could only be adequately explained by the existence of numerous rogue planes lying just outside the paths of the main thirteen in a place he called the Deeper Astral. According to Heirm's controversial theory these rogue planes interact with the main thirteen, and their courses tug and pull the fabric of the Astral Plane, explaining most of the cosmic complexity observed for centuries. He further theorized that while many rogue plans typically don't directly interact with Eberron, on rare occasions some could, and even proposed that one of these rogue planes may float close enough to Eberron to become coterminous. In his words, "Such coterminous states with these rogue planes are rare and wonderful events. If my calculations are correct, the next one will occur hundreds of years in the future. What such an event heralds is anyone's guess, as we have absolutely no idea of what ilk of creature could inhabit the rogue planes. I will just say this: Aryth in Tiamat they come. Then we will know for certain if I am correct in my calculations."
An utter libertine, prone to fits of rage and melancholy, many believed that Belental Heirm was insane at best, and possessed at worse. When he was implicated in a plot to assassinate King Jarot perpetrated by a cult of the Dragon Below, the fears of possession seemed confirmed. Heirm died a traitor's death at the hands of king's agents over 150 years ago.
Behind these clues, the team discovered a sinister plot cloaked in a web of disseat and subterfuge. For the past month Eberron was in a partial coterminous state with a strange realm outside the known cosmos called Spequlum. During this time, the strange race native to that realm, the nerra, had tangential contact with, and was able to view and communicate with, Eberron through mirrors in central Breland. Forging new alliances, these mirrored beings set the wheels in motion to infiltrate Eberron. To break the planer boundary, the nerra needed to rip a hole in the very cosmos and cosmic machine at Crook Observatory was capable of creating such a rift.
Among the nerra's allies was a dusk hag named Beltrudelgald. Tied by strange bonds of fate to the invaders, Beltrudelgald trailed Mayus Fellon for weeks, learning his habits, mannerisms, and secrets, while disguised as a young city goblin interested in the old man's work. When the time was right, she killed Fellon, took his identity, and gained control of the cosmic machine. With the help of misguided academics lead by Mers Vevel, a devotee of Belental Heirm's work, they modified the cosmic machine and allowed a single nerra sorcerer and his familiar to enter Eberron.
Gaunt, however, learned that something was amiss and meddled in Beltrudelgald's affairs. He escaped his confrontation with her at the observatory, but the hag's touch would be his end. Back at Grea Tower, Gaunt settled in for a night's rest to recover from wounds he received in the scuffle. Drifting to sleep, the hag's magic set to work, tormenting the digger with terrible nightmares. Wracked with terror, gaunt scribed the clue to his discoveries in his own skin before meeting his end among visions of horror.
Their plans delayed, Beltrudelgald and the nerra sorcerer, Nur-Zelmor, took new disguises and waited their next chance to activate the cosmic machine. Nur-Zelmor murdered Professor Vevel and adopted his form. The hag called on Mrs. Fellon and found a place for her fresh corpse in the pantry just in time to greet the enterprising diggers investigating Gaunt's death. Over tea and cucumber sandwiches, the false Mrs. Fellon played dumb, but the diggers pressed their case and her true nature was revealed. The team had already encountered and dispatched Nur-Zelmor disguised as Professor Vevel. They knew something was a miss with Mrs. Fellon. Overwhelming the diggers, the hag fled. All the clues now pointed to Crook Observatory. The diggers set out at once.
Drawing near the tower, a strange storm broke loose. Purple lightning licked the structure as the planer conjunction approached its zenith. The diggers knew they had to hurry. Fighting their way through the defenders left by Beltrudelgald, the diggers eventually reach the cosmic machine just as the nerra were beginning to cross into Eberron. With the controls to the machine smashed, several members of the team held the nerra emerging from three large, metal mirrors at bay, while the rest of the team raced to the top of the observatory to disable the Dragonshard that harnessed the storm's energy to power the cosmic machine.
With the machine disabled, the diggers repelled the invaders and secured the tower. After waiting for the planar storm to subside and the convergence to pass, the team returned to Grea Tower to recover from their exertions and report their findings to Matron Marta. Receiving the necklace and bound to silence one more pressing question remained, around which corner lurked their next adventure.