The Lost Tribe/Quick guide

Lumbridge cellar

 * of Lumbridge castle, talk to Sigmund.
 * Talk to the following NPCs about Lumbridge cellar until one of them mentions a goblin:
 * Duke Horacio, in the same room
 * Cook, just downstairs
 * Hans, in the courtyard
 * Father Aereck, in the church
 * Bob, in his axe shop
 * Return to the Duke (if you started or completed Dragon Slayer quest click option 4)
 * Descend the trapdoor in the kitchen and mine the wall rubble.
 * Go through the wall and take the brooch.

Dorgeshuun

 * Show the brooch to the Duke.
 * Talk to Reldo in Varrock Palace about the brooch.
 * Search the north-western bookcase for a goblin symbol book.
 * Read the book to the end.
 * Talk to Generals Bentnoze and Wartface in Goblin Village.
 * Return to the Duke.
 * Run through the cave (pictured right).
 * Use the goblin bow emote near Mistag.
 * Follow Mistag.

Making Peace

 * Talk to the Duke.
 * Pickpocket Sigmund.
 * Open the chest in the other room for a set of H.A.M. robes.
 * Talk to the Duke.
 * Enter the H.A.M. Dungeon, then search the crate near the entrance.
 * Return to the Duke.
 * Go through the Lumbridge cellar and follow Kazgar.
 * Talk to Mistag.
 * Quest complete!