Back and there again
Tannen will ask you for the Orb of Many Ways for study, and directs you to obtain (yet again) a Blood-Runed Athame and Resonating Diamond. You will go look in Reknor, as the orcs had a working portal. At the location of the portal you will fight a Lithfengel and he will drop the necessary items.
Upon returning to Tannen, he will ask you to check the Telmur, tower of Telos for a text on portals, while he works on building your new portal. In the tower you will find the Shade of Telos, who will drop the Telos's Staff (Bottom Half) but no book.
Upon returning to Tannen, he will reveal himself as a traitor and transport you to Tannen's Tower, where you will be forced to fight both him and the Dragon Golem. Defeating him will return the Orb of Many Ways to you. Upon exiting the tower, Meranas the Herald of Anglowen will greet and tell you they suspected Tannen (thanks, guys, next time stop him sooner?). He will then build the portal for you.
Note: This quest is a reference to "There and Back Again" AKA "The Hobbit", a book by famous author J. R. R. Tolkien.