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Aurifer knife puzzle (fuse box, mercury pool, moonlight)

Updated 17 Oct 2026 · Game version: launch version (Oct 16, 2026)

The answer in one line

Use the Lapis Fictus Knife on the kitchen fuse box (Melanosis Knife), climb down the elevator shaft and use it on the mercury puddle (Viridis Knife), try to leave through the hole so the TV drops the Lead Key, open the symbol door left of the 2nd-floor elevator with it, then use the Viridis Knife on the locked hotel door to get the Aurifer.

Missing something, or nothing happens? The steps are below.

Our pencil sketch of this puzzle goes here.
We draw the sketch once the puzzle is checked in a playthrough.

Where the puzzle is

The Desiderium is the corrupted version of the building that you enter after meeting Sanguis on the film set. This chain starts at its kitchen fuse box, goes down the elevator shaft to a pool of mercury, then back up to the studio lobby and on to a hotel door.

The Old Book gives the recipe: the blade is revived by electricity, dipped in the mercury pool at the deepest point (the Putrefactio stage) and bathed in moonlight. Each step changes the knife's name.

Before you go on: once you hold the Aurifer, Relicta ghosts line the route to the finale. Killing even one of them with the Aurifer locks you into Ending 2 (MAGNUM OPUS); sparing every one gives Ending 1. Save before the finale route. See the endings page.

Not sure you’re in the right place? Search for your room in Quick find tool.

What you need

  • Lapis Fictus Knife: from the Iván statue at the end of the Lapis Fictus Knife puzzle
  • Lead Key: dropped by the TV in the elevator shaft once you try to leave through the hole

Exact spots for each one are on Items and collectibles.

Step by step

  1. Charge the knife at the fuse box

    Use the Lapis Fictus Knife on the fuse box in the kitchen. It becomes the Melanosis Knife.

    Old Book page 16 in blue text warning that the Lapis Fictus shortcut will compromise your soul
    Frame from “Tenebris Somnia - All Puzzles & Solutions Guide” by iampanax. Watch at 50:20

  2. Climb down the elevator shaft

    Go down the elevator shaft. Relicta ghosts are down there; don't fight them, just run.

  3. Dip the knife in the mercury

    Use the Melanosis Knife on the mercury puddle at the bottom. It becomes the Viridis Knife.

  4. Make the TV drop the Lead Key

    Try to leave through the hole. The TV drops the Lead Key; pick it up.

  5. Open the studio lobby symbol door

    Back on the 2nd floor, use the Lead Key on the door with the symbol to the left of the elevator, in the studio lobby.

  6. Use the Viridis Knife on the hotel door

    Keep heading north to the locked hotel door and use the Viridis Knife on it. A cutscene plays and the knife becomes the Aurifer.

If it doesn’t work

The Relicta ghosts keep catching me in the elevator shaft.
Don't stop to fight. Keep moving to the mercury puddle, use the knife and head for the exit.
I have the Viridis Knife but no Lead Key.
The key only appears after you try to climb out through the hole. Go back to it; the TV drops the Lead Key then.
I accidentally killed a Relicta after getting the Aurifer.
That run is now headed for Ending 2. Reload a save from before the finale route if you want Ending 1.

Sources

  1. Tenebris Somnia - All Puzzles & Solutions Guide by iampanax Timestamps used: 50:11–52:50
  2. Tenebris Somnia Full Game Walkthrough - All 4 Endings [No Commentary] by iampanax Timestamps used: 3:53:20

Spotted a step that’s wrong? Tell us and we’ll fix it and update the date.

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