Before the story of the Wanderer begins in Diablo 4, Lilith is summoned back to Sanctuary by Elias. This event sets into motion the story of the game, as you and your ✤allies chase Lillith and Elias around to various locations, trying to stop their plan.
In the To Walk a Dark Path side quest chain, you can learn a bit more about how Lilith was summoned to Sanctuary. This chain is comprised of four quests, ending with By Three They Come, which we will take an in-depth look at below, including how to startꦏ it and how to finish it.
How To Complete By Three They Come Quest
By Three They Come is the final quest in the To Walk a Dark Path quest chain, and is automatically accepted after completing the previous quest, Turbulent Waters.
To start, meet with Sev to the west of Backwater. The closest Waypoint is the one in Vyeresz, which will be accessible if you've cleared the Stronghold here. Once you've reached Sev's location, talk with her to get her to accompany you.
Next, travel a bit more west to the Esret Chapel. When you arrive, Sev will leave your company and the mini-dungeon Halls of Dark Portent will become available. Enter this du🦋ngeon and make your way through, killing enemies that get༺ in your way.
Eventually, you will make it to an Engraved Stone Door. As you start to attack this door, Ghouls will ambush you. Fend them off to resume damaging the door. This will occur two more times; fight off each wave of Ghouls as they appear. Soon, you will destroy the Engraved Stone Door, permitting you entry into the next area.
Behind the door is the Blood Echo boss. This boss functions almost exactly the same as the Blood Bishop boss that you may have encountered in other dungeons like Akkhan's Grasp or Hallowed Ossuary.
The main thing to keep in mind during this fight is the boss's ability to grab and hold you in place, dealing constant damage. Having an ability that can make you Unstoppable will help you escape this dangerous attack.
After defeating the boss, inspect Symon's corpse and read the Tattered Journal that he drops. Travel back to Zarbinzet to relay everything you've learned to Father Dymus, and this quest will be complete. In addition to the normal quest rewards of gold, experience, and Renown, you'll also gain the 'Pale Harbinger' title.