The Guild met the OotS seemingly by chance, and they decided to join and split forces for each of the sigils. Nale made sure that the Good members of the OotS activated the sigils. Then a door appeared that led to a great vault where the Talisman was kept, with many types of monsters around it.
Nale stole the Talisman and attacked the Order; Thog cleaved the platform of the protective runes and they flew away, leaving the Order stranded. But then Haley Starshine destroyed the Talisman with a lucky shot that severed its chain and caused it to plummet to the ground. This made the monsters go astray and the Guild was forced to fly back to the platform where they ensued in a fight with the Order. Whats left of the pieces would presumably be destroyed with the destruction of the Dungeon of Dorukan.
It was designed to "herd" all the obsolete 2nd Edition monsters (such as Dracolisks, Death Dogs, Guardian Daemons, Osquips, Wolves in Sheep's Clothing, Hordlings and Flumphs) into the vault, while magical runes prevented the monsters from attacking.
It was protected by three magical sigils, one representing each of the classical elements (except water, since apparently there were budget issues towards the end of dungeons construction). Each rune was at the end of a dangerous stretch of dungeon thematically tied to one of the elements in a dreadfully clichéd manner. Each of the sigils needed to be touched at the same time by a Good alignment in order to open the path to the talisman.