The Forgotten Thief is a story quest chapter for Lyney in Fontaine of Genshin Impact.
Your objective is to investigate the Phantom Weasel with Lyney.
Here’s a walkthrough and guide of The Forgotten Thief in Genshin Impact.
This guide will be subdivided into several quests.
The Phantom Thief’s Reappearance
The first quest is The Phantom Thief’s Reappearance.
To start the quest, you have to unlock Lyney’s story quest first. Then, head to the Gem Merchant as marked in the map below.
Talk to Charlotte from The Steambird.
During the cutscene, you’ll meet Lyney nearby.
Next, head to a cemetery as marked in the map.
Go to the cemetery to find Jemma who is Cesar’s wife. Cesar was a renowned magician 10 years ago who died.
Ask around the area for more information.
You’ll then meet Jemma in the cutscene.
The first quest ends here.
The Magician’s Secret
The next sub quest is The Magician’s Secret.
Change your time till next morning (08:00 – 12:00).
Then, go to the hotel to meet Lyney.
Enter the hotel to talk to Lorenzo who used to be Cesar’s disciple.
After the conversation, leave the hotel and find Edmondo outside.
As Lyney detects they’re getting followed, you have to leave the city. Head to the quest marker.
Lure out the people who are tailing them.
As they appear, defeat the people who were tailing.
Head back to the city to find Jemma and Lynette. Inform them of what had happened.
Next, go to the sewers area where Spina di Rosula is.
Head to Cesar’s workshop which is marked on the map.
Enter the Magic Workshop via the hatch on the floor.
In the first area, jump to the left platform and switch to the right to cross over.
You’ll then see some of Cesar’s gadgets. Hit the toys that come out of the box to fix them there. Hit both and the door opens.
Continue ahead and defeat the enemies.
You’ll reach more gadgets. Hit the gadgets again to open the door.
Use the elevator to go up.
You’ll reach more mechanisms. Start the first one on the left.
Observe the four gadgets and you’ll see one of them glowing.
Follow the movement of the gadget and hit that particular one.
Now, start the device on the right and do the same thing.
After you’re done with it, a secret door opens. Enter the area.
You’ll meet more enemies. Take them down.
Keep going and clear the area from enemies.
You’ll then need to solve a puzzle.
Start the device and you’ll see all the tiles lit.
Basically, you need to step on every tile only once and complete the puzzle.
I started from the other side and went one round.
To avoid stepping on the same tile, you can actually jump and use the moving tiles in the middle to move around. The protruding tiles on the opposite end can be reached by jumping.
After solving the puzzle, investigate the room for Cesar’s diary.
Leave the area and head to Lyney’s location.
Before exiting, Lorenzo shows up with his henchmen.
Defeat Lorenzo’s men.
Get the chest after the battle and leave the workshop.
Go back to Jemma and Lynette to explain the situation.
The quest ends here.
The Truest Thing
Third quest The Truest Thing begins here.
Go to the opera to watch the magic show.
Head to the front seats and you’ll see Lynette and Jemma there.
During the intermission, Lynette tells Jemma she knows the latter is actually The Phantom Weasel.
Go to the back of the opera to ask about the truth.
After ascertaining the truth, leave the building from the front to watch the high-altitude escape trick.
Lyney then performs the magic trick successfully.
After the act is done, go to the cemetery to meet Lyney.
The fourth quest The Interview begins here.
Change the time to (08:00 – 12:00).
Head to The Steambird’s offices to meet Lyney, Lynette and Charlotte.
The quest ends after the conversation.