Cain, in a bizarre plot twist, appears to be the only person On the Planet which can read the Horadric scroll. Strange. He tells you of the seal to the Horadric Tomb, which holds Tal Rasha. The lock must be opened by a Horadric Shaft topped by a Horadric Headpiece. You have to join these two parts togeter with a Horadric Cube. Right. Your current quest is to find those pieces.

Your quest log tells you where each piece is. The Cube is in the Halls of the Dead, under the Dry Hills. The Shaft is in the Maggot Lair under the Far Oasis. The Headpiece is in the Claw Viper Temple. Off you go!

Halls of the Dead is very easy - that's in the Dry Hills map area, the second one in. The Far Oasis is a bit further in, and the Claw Viper Temple is off the Lost City map area. When you get all 3 pieces, you stick the headpiece and staff into the cube and voila! It merges into the staff.

The quest doesn't officially end until you get out to the correct tomb and stick the staff into the orifice, and kill the nasty beast in the next room!

Diablo 2 Walkthrough
Walkthrough Master Index