It turns out Tristam is pretty much a smoking hole in the ground now and poor old Deckard "Stay awhile and listen" Cain needs to be rescued. Akara will tell you of the quest; it's a two parter. The first part is to retrieve a scroll from the Tree of Infuss and bring it to Akara for translation. The tree can be found in the Dark Woods. Get to the Dark Woods by heading through the Stony Field to the Underground Passages, leaving the passages puts you in the Dark Woods.
While on the Stony Field, you'll need to find the Cairn Stones. This is where you will return with the translated scroll, it will tell you the order in which to touch them. Secondly you'll need to find the "moldy Tome" which will give you Quest 4. Don't forget to also activate the waypoints in the Stony Field and the Dark Woods, you'll be coming this way again.
Upon activating the Cairn Stones, a portal will open to Tristam. Here you can rescue Deckard Cain by touching his pen. Cain will make a quick escape, leaving you to either run back to the portal or clear the level out. The baddie you'll fight here is none other than a cursed Griswol he is tough so be ready to move to safety if overwhelmed. Don't forget to find that bratty price gouger Wirt's cash and peg leg -- sweet revenge for all the cash you gave the lil' bastard in the first game. Head back to town when you're ready.