The 13th floor of the Obsidian Tower isn't technically inside the tower. Instead, it leads to the Obsianus House, a private four-story manor house located in Sigil, City of Doors. The House can be found in the city's Guildhall and Markets Ward.
The house is presided over by the male tiefling Jith Vendhzar (Wiz 10/Loremaster 5), an old loremaster well-versed in the secrets and factions of Sigil. He no longer ventures into the field; those expeditions he leaves to his two seconds: the female human cleric of Boccob, Aynmarenn (Wiz 12/Clr 5) and the planetorn survivor swordsage Zilanderan (4E Wiz 15).
Zilanderan is a new to the Obsianus House. He arrived through its "Prime Door" -- the house's connection to the Prime Material Plane -- in CY 590, half-crazed and raving about stories of the Fall of Obsidian Bay to rampaging hordes of slaads. he described the subsequent loss of the entire plane to the forces of Chaos in such stunning detail that Jith immediately dispatched mages back to the Prime to discern what happened for themselves.
The Prime was intact. But the incident soon proved not to be an isolated one, as reports of invasona and distruction began to trinkle in from the farthest reaches of the multiverse. Zilanderan was soon sworn into the True Tower, and charged with leading up a task force to investigate the strange invasions.
To that end, he has begun assembling groups of Planetorn, those with a vested interest in discovering who is responsible for the invasions ... and stopping them. He's assembled a half-dozen teams to travel through portals to alternate material plane, obscure demiplanes, distant planar locations.
- Aynmarenn (Wiz 12/Clr 5) the female human cleric of Boccob
- Jith Vendhzar (Wiz 10/Loremaster 5), master of Obsianus House
- Thrax, a Dragonborn Wizard, and planetorn refugee who now works for the Obsidian Tower
- Zilanderan (4E Wiz 15), planetorn investigator