If you're after completing this achievement ASAP, open the spoiler. If you are after enjoying the story without spoiler, just continue playing as you would and this will eventually unlock.
*** Spoiler - click to reveal ***
You'll start where the previous episode left off, moving down a tower. You'll end up in a whole new underground world, the first world. There's not much time to explore, as you'll soon get attacked by a giant enderman. Follow the evasive prompts and move down the tower. Xara's city is on the other side of the hills, so better get moving!
Xara will lose it once you get to her town, her bed is gone. Just follow the dialogue and make choices until you hear Petra asking for your help. Take care of a few spiders and of the 3 creepers. You'll be heading to Fred's keep afterwards. Head over to the minecarts to complete the first chapter.