Bound By Flame The Soul Of A Prince is the first side-quest you can trigger in the fourth act of the video game, when you enter the Sewers with Rhelmar.
The Soul Of A Prince; however, can be completed only after you start the second chapter of the same act, because you will need to defeat one of Blackfrosts Concubines.
When you enter the Sewers and start The Lions Den, you will be asked to reach the Makeshift Camp. While following the tunnels, eventually, you will enter a round room where you will see a pile of corpses.
As you go around the pile, if you pay attention to Rhelmar you will hear him telling you that there is something strange with one of the corpses.
If you face the eastern tunnel, turn around and approach the corpses to find Arandil, the Elf Prince.
Rhelmar will eventually ask you to find a way to get close to Arandils body, but you should postpone the quest for now and focus on finishing The Lions Den, so you can start Chapter 2: Witch Hunt.
Bound By Flame Walkthrough The Soul Of A Prince Quest
When Witch Hunt begins your objectives will be very clear. In order to defeat Blackfrost you have to fight three Concubines.
The Concubines can be found in Blackfrosts Domain, and their locations coincide to the locations where you have to complete The Soul Of A Prince and The Blades Enslaved.
You have to be aware that there are three Concubines, and only two areas you have to reach, which means that in one area you will fight two Concubines.
The trick is to visit the western side of Blackfrosts Domain and deal with the two Concubines that allow you to continue The Soul Of A Prince, because if you attempt The Blades Enslaved first, you will fight more enemies. When you enter the battleground you have to know that the Concubines spawn several Deadwalkers.
First kill the archers, then the remaining Deadwalkers. Now target one Concubine and observe that you cant hurt her. Thats because if you attack one Concubine, you deal damage to the other one.
Tip: Once you start attacking one Concubine, stick to your target, and dont switch between them.
Again, you will be able to defeat the two Concubines faster if you use arrows, but you can also place traps and wait for your targets to get close to them. Staying mobile is very important in order to avoid incoming projectiles.
After you kill one of the Concubines, use the same tactics to defeat the other one and win the battle. When you complete the battle, return to the Makeshift Camp and talk to Rhelmar.
Ask him to join your party, then return to the Sewers and to the pile of corpses. Retrieve Arandils Elf Soul, and Rhelmar will tell you that he needs to perform a ritual for hid prince.
Take him to the entrance of the Sewers, where you have started the third act. To complete the quest, check the left side of the tunnel, very close to the entrance to start the ritual, and watch the final cutscene.