Watch the cutscene after leaving New Tristram. Leah thinks her uncle's journal is all stories. That he only saw what he wanted to see. Tyrael tells her that Deckard sacrificed much to protect this world, but his work is not over. When Leah asks Tyrael what he would know about sacrifice, he shows her a vision. A figure in the Heavens, Imperius, is telling Tyrael that the law of the High Heavens strictly forbids them from interfering with the mortal world. Tyrael says that all he was doing is bringing justice and accuses Imperius of hiding and cowering behind the throne. After a struggle between him and Imperius, his brother, Tyrael chooses to sacrifice his immortality, and falls into the mortal world. Tyrael did this because he believes humanity is the only hope for this world. This convinces Leah to finish the work that her uncle, Deckard Cain, began.
Tristram is safe, and you travel to Caldeum , the Great City of the East. It has fallen before one of the Last Lords of Hell, Belial. You will set the city free.
You should be getting the following achievement at this time:
The Last of the Horadim
Complete all quests in act I
Follow the desert trail to the north. You arrive at the Hidden Camp, located on a cliff high above Caldeum. This will be your main base of operations for Act II (Similar to what New Tristram was in Act I). Your two followers (Scoundrel, Templar) and the Artisan Haedrig Eamon (Blacksmith) are also here. Your Stash is here too, note its location.
Speak to Leah to set the first quest of Act II in motion. She tells you that Caldeum is the Jewel of the East, and how Uncle Deckard loved this place. Tyrael notes that Caldeum is now under the spell of Belial, Lord of Lies.
You receive the quest:
Shadows in the Desert
Go to the Caldeum Bazaar
Locate the exit to the Caldeum Bazaar at the Northeast section of the camp. When you enter the Caldeum Bazaar, talk to Asheara. She tells you she is not a guard, she is the Commander of the Iron Wolves. They saved the refugees from Maghda's Coven, that even now wreaks havoc throughout the Borderlands. You ask her where you could find Maghda. Asheara tells you that Maghda is heading towards Alcarus, but has blocked the road behind her. However, there is sill another way: through the Khasim Outpost.
Your next objective is to go through the Sundered Canyon.
