The Lost Tribe/Quick guide

Walkthrough

 * Start by talking to Sigmund.
 * Talk to the duke, cook, Hans, Father Aereck, Donie, and Bob. One will mention a goblin in the basement.
 * Talk to Sigmund again, then the duke.
 * Use your pickaxe on the rubble in the basement.
 * Light your light source and grab the brooch.
 * Show the brooch to the duke.
 * Go to Reldo, the palace librarian in Varrock.
 * Search the bookshelves for a book on goblin history. (Northwest corner, on the west wall)
 * Read it to see that the symbol on the brooch translates to "Dorgeshuun, goblins of the strong spears".
 * Talk to the Goblin Village generals, mediate for them until you learn goblin emotes.
 * Go back to Lumbridge, and talk to the duke. He will tell you to investigate the caves further.
 * Follow the map through the caves. Don't stray from it!
 * At the end of the cave talk to Mistag, and do your Goblin Bow in front of him.
 * Talk to Mistag then let him take you back to Lumbridge.
 * Talk to the duke, he won't believe you.
 * Pickpocket Sigmund and unlock his chest in the other room to find some HAM robes (keep them for later)
 * Tell the duke that Sigmund is part of Humans Against Monsters.
 * Go to the HAM lair (west of the general store; pick the lock)
 * Search the crates in the first room to find the stolen silverware.
 * Bring the silverware to the duke. He will fire Sigmund and give you a signed peace treaty.
 * Go into the basement again and talk to the goblin there to be taken to Mistag.
 * Talk to Mistag.
 * Quest complete!