The Stench of Treachery quest in "Assassin's Creed Valhalla" is one f the longest quests. Eivor must find out the traitor in Grantebridgescire and figure out who betrayed Soma. it is important to choose the right traitor because it has further implications in the main story; for those who need help in deciding who that traitor is, this guide could come in handy.
In "Assassin's Creed Valhalla," Eivor travels south to pledge to Grantebridgescire and forge an alliance with the Jarlskona of Grantebridge: Soma. Unfortunately, there is a turncoat that Eivor has to uncover for Soma, and it involves the three trusted advisors Birna, Lif, and Galin. The tough part is, Eivor will have to call that final decision, and to do that, he must investigate to learn about the motives of the traitor.
Investigate the Grantebridge Tunnel
After speaking with Soma, Eivor will find a secret tunnel within the Grantebridge longhouse. He has to climb down the ladder but needs to use Odin's sight along the way. Eivor will find a yellow cross and some footprints with drops of paint leading away at the tunnel entrance. Eivor must follow the trail that will lead to the discarded paint and a longboat by the river.
Gather Intel from Villagers
Eivor could also start the Stench of Treachery quest in "Assassin's Creed Valhalla" by collecting information from the villagers. These characters have speech bubbles hovering above their heads. They could offer crucial information that Eivor could take note of.
This includes Birna, one of Soma's trusted advisors, was drinking the night before the attack. Eivor will also learn that more information could be uncovered in Meldeburne. Additionally, he will learn that Lif inscribed poetry inside of the longships he builds. Most of these ships were lost in the Fens following the attack.
Travel to Meldeburne
In Meldeburne, Eivor could attack the area to set the caged allies free. There is a chapel with a note that reads, "Do not fire upon the longship painted yellow. That vessel carries the herald of our great victory." The traitor painted their ship yellow, and locating that ship could help gather more pieces of evidence.
Raid with Birna, Lif, and Galinn
While raiding with Soma's trusted advisors, Eivor will learn that Galinn believes he is fated for greatness from the Gods. He is also fanatical of his visions. It appears that Birna has an unrequited love for Soma. Meanwhile, Lif is in charge of the clan's longboats like the one Eivor found by the river, but he claimed it was stolen. Lif also disagrees with how Soma runs things and wishes that he had led Granterbridge.
Find the Yellow Longship
The yellow longship will help Eivor find the traitor. Sail towards Fens, and to the left, he will start finding crashed ships. Examine the ships, and Eivor would find Lif and Birna's ships, and going further will bring him to Galinn's ship, which has yellow paint on it. Now for the element of deduction to come into play.
When Eivor rescued the three advisors in the swamp, Lif and Birna were surrounded by other members of the Soma clan. Essentially, if both fled by the tunnel's entrance, all their crew is a part of the deception. However, Galinn was alone and was trapped by a pack of wolves. Aside from the yellow paint on his longship, Galinn could be the one who used the tunnel's entrance, and therefore the traitor of Grantebridge.
"Assassin's Creed Valhalla" is now available on PlayStation 5, Xbox Series X and Series S, PlayStation 4, Xbox One, Google Stadia and Microsoft Windows.