The hoop was essentially a huge frame made of iron, taller than a human, such that one could pass through the device. The device was attached to a stand and roller, and similar to one a trainer of great cats would use. A symmetric spider web filled the hoop's interior, which appeared fragile, but the strands were incredibly strong and magically powered. When one passed through the hoop, a part of their life force would drain away.
In 1356 DR, the Calimport guild led by Pasha Pook owned the device. LaValle, the wizard of the guild, could both scry on beings of his choosing, such as the Companions of the Hall, and also peer into other planes, as well as travel to them.
Later, the companions reached Calimport to rescue the halfling rogue Regis from his former guildmaster, Pasha Pook. Guenhwyvar, Drizzt's panther, refused to obey commands from Pook, and returned to its home in the Astral Plane, and LaValle showed his master, Pook, an image of the panther through the hoop. LaValle then showed Pook images of the companions tearing through a small army of wererats guarding the thieves' guild hall, where Pook and LaValle resided in the uppermost floor.
Upon the command of Pook, LaValle uttered an incantation to use the Taros Hoop to send the companions to a "dark place," in this case, the Plane of Tarterus. Regis, realizing that his friends had fought their way through the wererats to save him, tried to escape by stealing Guenhyvar's statue and the command scepter, and jumped through the hoop as LaValle finished the incantation to banish the rest of the companions to this plane.
Through much struggle, the companions managed to recover Regis, the scepter, and the statue of Guenhwyvar (who escaped with Regis back to the Astral Plane, and rallied a small army of astral panthers). They returned through the gate from the side of Tarterus, through the hoop, back into Pook's chambers on the Prime Material Plane. The barbarian Wulfgar attempted to close the gate by bending the metal of the hoop, while fighting off demodands attempting to come through the gate, but he was unable to because of the intense magic of the hoop itself.
As the last of the companions returned through the portal, Wulfgar released the Hoop, grabbed the scepter from Drizzt, and smashed it at the same time that LaValle cast a spell into the gate, shattering its magic. A brief cloud of darkness filled the room, and when it dissipated, only a broken hoop of iron, dripping with interplanar goo, remained. The panthers from the Astral Plane returned to the guildhall to finish off the wererats and Pook. After Pook fell, Regis became the master of the guild in Calimport.