Leads to the quest: Kirith: https://vanillawowdb.com/?quest=2721 https://vanillawowdb.com/?quest=2721

This is a quest in a chain of 23 that runs pretty much all over the map.
However, it all starts with the Fallen Hero of the Horde.
(Hat tip to Xeir for the initial connectors between chains.)

Technically, it's four chain quests that tie into each other:
Chain 1:
1. https://vanillawowdb.com/?quest=2784 Fall From Grace
2. https://vanillawowdb.com/?quest=2621 The Disgraced One
3. https://vanillawowdb.com/?quest=2622 The Missing Orders
4. https://vanillawowdb.com/?quest=2623 The Swamp Talker

Chain 2:
1. https://vanillawowdb.com/?quest=2783 Petty Squabbles
2. https://vanillawowdb.com/?quest=2801 A Tale of Sorrow
3. https://vanillawowdb.com/?quest=2681 The Stones That Bind Us
4. https://vanillawowdb.com/?quest=2702 Heroes of Old
5. https://vanillawowdb.com/?quest=2701 Heroes of Old

Chain 3:
1. https://vanillawowdb.com/?quest=2721 Kirith
2. https://vanillawowdb.com/?quest=2743 The Cover of Darkness
3. https://vanillawowdb.com/?quest=2744 The Demon Hunter
4. https://vanillawowdb.com/?quest=3141 Loramus
5. https://vanillawowdb.com/?quest=3508 Breaking the Ward
6. https://vanillawowdb.com/?quest=3509 The Name of the Beast
7. https://vanillawowdb.com/?quest=3510 The Name of the Beast
8. https://vanillawowdb.com/?quest=3511 The Name of the Beast
9. https://vanillawowdb.com/?quest=3602 Azsharite

Chain 4:
1. https://vanillawowdb.com/?quest=3621 The Formation of Felbane
2. https://vanillawowdb.com/?quest=3625 Enchanted Azsharite Fel Weaponry
3. https://vanillawowdb.com/?quest=3626 Return to the Blasted Lands
4. https://vanillawowdb.com/?quest=3627 Uniting the Shattered Amulet
5. https://vanillawowdb.com/?quest=3628 You Are Rakh'likh, Demon

Completing the entire chain gives you the following:
103,685XP at appropriate level
Shard of Afrasa
Enchanted Azsharite Felbane (Dagger, Sword or Staff)
Necklace of Sanctuary
Demon's Blood
Demon Hide Sack