During The Kayran: Ostmurk main quest included in the first act of The Witcher 2 Assassins of Kings Enhanced Edition video game, you have the chance to activate a side-quest named Mystic River.
To do so, make sure that you investigate the shipwreck located in the swamp where you found the Kayrans mucus.
On the left side of the boat is a key which opens a chest located on the right side of the ship. Loot that specific chest to trigger the Mystic River side-quest.
Quest Description
In the monsters lair, Geralt spotted the wreck of a large riverboat. Within its shattered hall lay a corpse which, as it turned out, was that of the boats captain. On the corpse, Geralt found a key. Picking it up, he instinctively looked around for the lock that might open.
The key the Witcher found on the corpse matched a rusty chest nearby. In it, Geralt found the journal of the Petra Silies captain, and a copy thereof packed for shipment to the University of Oxenfurt. Our hero concluded that the captain had intended to provide a report of his journey, but failed to dispatch the manuscript for unknown reasons. The Witcher decided to do him that small favor using the Royal Mail that all Temerian officials could access. And who was, by the kings will, the ranking official in Flotsam? The answer to this question was simple.
When to start
After The Kayran: A Matter of Price
Walkthrough
As soon as you get the box, return to Flotsam and look for Louis Merse. He is the one who paid you for completing The Nekker Contract and The Endrega Contract.
Usually, you will find him inside his house, located in the town square. The house has two green tents in front of it, tents used by vendors.
Go upstairs and check his desk where you will find a box, but you will need a key. Persuade Louis to give you the key and place the reports. Next, take a closer look at Merses report. The quest will update as soon as you complete the first objective.
The second phase of this quest can be completed while playing Death to the Traitor! main-quest, Indecent Proposal or The Floating Prison.
The quest continues in the second and the third chapter of the game, as follows:
Chapter 2 - Iorveths Path
If you ally with Iorveth at the end of the first act, you will be able to play a side-quest called Baltimores Nightmare. At the end of this specific quest, you will have to find a secret laboratory (near Vergen) which belonged to a runesmith called Baltimore.
Next to the laboratory’s secret entrance you will find another shipwreck containing a chest. Inside the chest is the Journal from the Eyla Tarn, which allows you to progress through this quest. Follow the Baltimore’s Nightmare walkthrough for the exact location.
Chapter 3 - Iorveths Path
While playing For A Higher Cause! quest featured in the third chapter, you will have the chance to explore the sewers under Loc Muinne. In the northern area you will find two chests, using Geralts medallion.
One of them contains the diagram for Armor of Ys while the other one contains the diagram for Vran Armor.
Take the diagrams to Bras of Ban Ard in the southern area of Loc Muinne. Bras of Ban Ard is a nobleman wearing a blue tunic and a red hat with white feathers
Ask him to craft an item for you and select the Armor of Ys. Using the new armor as a crafting material, ask Bras of Ban Ard to craft the Vran Armor. Equip it to complete the Mystic River quest.
Note: Both armors are very expensive and very powerful. For the second one you need 2000 Orens, while for the first one, you need 30 robust cloth, 12 studded leather, a troll skin, 5 Nekker claws and 10 twines.
You also have to pay 825 gold, so the grand total for Vran Armor is 2825 Orens and a lot of materials. Without this specific armor you cant complete the quest.
