The meeting can be found at 6717, 1141. Make sure to receive credit for "Interrupting the meeting" before killing any of the participants. The meeting consists of Brahl Darkfall, Lisandra Cavrin, and Dashe Teel. All three of them are level 40 elites so it is highly recommended that you bring a party. After slaying the three collect the Spellbook of Corthana.
To see the whole quest series at a glance, see The Saga of the Endless Guide .