Under Lock and Key

Under Lock and Key was a virtual representation of one of Arno Dorian's genetic memories, relived by a Helix initiate through the Helix Navigator.

Description
With the correct keyhole revealed, Arno only needed the key to the temple door.

Dialogue
As Léon jumped over the wall into the orphanage courtyard, Arno arrived. As Arno left, so did Léon. Reaching the market, Arno found the lieutenant with his men. Arno tailed the lieuteenant. The lieutenant entered a building and spoke with a raider. As the lieutenant ran away, Arno chased and caught him. The lieutenant gave Arno the key to the chest. Entering the catacombs, Arno found the raiders' hideout. The raiders detected him. Arno stole the raiders' loot, inciting a riot among several of them. This made his infiltration easier. He then killed an orator speaking to the raiders, causing a panic among those listening to him. Eventually, Arno found Napoleon's chest and unlocked it, taking the golden key within. Arno escaped the catacombs.
 * Léon: (Hello!)
 * Arno: What have you been doing?
 * Léon: Nothing. Did you find the lock?
 * Arno: Yes. Now I need the key.
 * Léon: You know the soldier carrying the chest for the little commandant? I just saw him in the market.
 * Arno: (Thank you.) And I told you to stay here, remember?
 * Léon: "(Yes, sir.)"
 * Arno: There you are. Now lead me to the golden key.
 * Lieutenant: Alert me if you see anything unusual.
 * Soldier: Yes, sir.
 * Lieutenant: What do you have for me this time?
 * Raider 1: Silver, nearly enough to fill a chest.
 * Lieutenant: Give it to me.
 * Raider 1: The Commandant still suspects nothing?
 * Lieutenant: He is occupied in Paris. Your usual fee, plus a promotion.
 * Raider 1: Tres bon. A pleasure doing business with you.
 * Lieutenant: Guards! I will have you arrested!
 * Arno: You will do no such thing. Tell me the location of the chest containing the golden key or I shall reveal your thievery.
 * Lieutenant: I am merely seeking a harmless profit.
 * Arno: Like a rat hungry for apples?
 * Lieutenant: How did you know-
 * Arno: Surely the Commandant will find the comparison... enlightening.
 * Lieutenant: The chest is under guard within the caverns. Here.
 * Arno: Merci. Now get out of my sight.
 * Raider 2: Invader! We will find you!
 * Arno: All that security for a key. What lies behind that door?

Outcome
By blackmailing Napoleon's lieutenant, Arno was able to unlock the commandant's chest. In it, he found the golden key to the temple door.

Reference

 * Assassin's Creed: Unity - Dead Kings