From the first page of the PDF:
A noblewoman fears that her nephew is lost on a fool’s errand into the dreaded Undermountain, and she turns to a group of adventurers to rescue him. The first step is to make the entrance safe. A Living Forgotten Realms adapted adventure set in Waterdeep and Undermountain for Adventure Level 2 (which supports character levels 1-5). This adventure is found in the Halls of Undermountain sourcebook, available at retain game stores and bookstores.
This adaptation document does not present adjusted stat blocks for various tiers; any legal AL 2 table can play, but bear in mind that the stat blocks in the published adventure were written for a party of level 1 characters. We recommend that you allow at least 16 hours of playing time to complete this adventure (the equivalent of a four- round LFR adventure).