Received from: Automatically after talking with Dethmold during The Blood Curse.
Step 1: Ask about Vandergrift's sword on the other side of the mist
Complete the part of The Blood Curse in which you get through the mist.
After reaching Vergen, you will be stopped by Cecil Burdon and Skalen Burdon (M27, 1) beside the gate. Ask them about the sword and Zoltan will end up with the task of obtaining it. You are to meet him in the tunnels below Vergen.
Step 2: Meet with Zoltan in the tunnels below Vergen
As you go through the tunnels, you will come across a few types of monsters - Nekkers, Rotfiends and even Bullvores (M29, 2) - you will have to face one of them on your way to meet Zoltan and Saskia (M29, 3). The virgin of Aedirn will give you the Vandergrift's sword without making any problems. You will also learn that the spearhead is now in possession of Skalen Burdon and not Iorweth.
You will unlock The Spear of Destiny.