Dragon Age II- Mark of the Assassin
In the second major DLC pack for Dragon Age II, Tallis joins the party when she rescues Hawke from a pack of Antivan Crows that had used Varric's contacts to reach the Champion of Kirkwall. Tallis came to Hawke with a proposal; she needed someone who could get into the Orlesian castle, Chatteau Haine, run by Duke Prosper. Within the castle was a jewel, the Heart of the Many, which Tallis said he had no right to possess, and she needed help taking it back. Hawke had forgotten about the invitation that was given to him/her after the defeat of the Arishok, but agrees to help the elf. When they arrive at the Orlesian castle, Prosper happily accepts them as guest of honor, and sends them out with the other guest to hunt down and kill a local Wyvern. With Tallis' help, Hawke is able to attract a massive Wyvern, and kill it, allowing them to return to the party as the group of the hour.
Once inside, Tallis pretended to be Hawke's date long enough to steal a key to get the two into the castle itself. Sneaking past servants, cooks and Prosper's army, the two fell into Prosper's trap; the Orlesian Duke knew exactly who Tallis was the second she stepped foot in the Castle, and identified her as a follower of the Qun, to Hawke's surprise. He then threw the two in his dungeon, forcing Hawke and Tallis to wait for the other companions help; taking up the time by talking about her role as a Qunari, and Hawke's opinions on the fact. Eventually, Tallis got bored and simply picked the lock open moments before the rest of the party could reunite with Hawke. They continued to sneak out of the Castle, and were forced to fight and kill Prosper's Chasind guard in the process.
Tallis soon revealed that the Heart of the Many was a rough translation of the order of assassins employed by the Qunari, a group she had formerly belonged too, and hoped to return to because of her quest. She told Hawke that her real target was a Qunari turn-coat, Salit. When the two corner Salit, it is too late, and he hands over a list of vital Qunari information to Duke Prosper; a list of names. Confused, Prosper raged that he was promised a weapon, and without bothering to question the purpose of the names (and accidently handing the scroll over to Tallis in the process) he orders his troops to butcher the Qunari, killing Salit before turning to Hawke and Tallis.
With their combined might, Hawke and Tallis overcome Prosper, who calls in his pet Wyvern for help. In the end, his mount is not enough to win the day, and Prosper fell to his death off a cliff, cursing Hawke as a filthy, Ferelden "turnip". Tallis told Hawke that the list contained the name of every Qunari agent, past and present, hidden in Thedas. She was thankful this information remained safe thanks to Hawke's efforts, and took the scroll to return to the Qunari or destroy. With that, she walked out of Hawke's life forever.
However, her presence did not go unnoticed, and when Cassandra was interrogating Varric Tethras about the events of the Mage-Templar war, she interrupted his story to demand what had happened, revealing that as a result of Hawke and Tallis' deeds, the Orlesians are ready to start a war, though Varric was surprised that Cassandra knew who Tallis even was. With no other choice, the dwarf bard began to tell the Seeker everything he knew about Tallis and the event in question.