The Velvet Curtain

The Velvet Curtain is a side quest in the Fallout 3 add-on Point Lookout.

The quest leads the Lone Wanderer to find the whereabouts of missing Chinese agent Wan Yang, and use the Submarine self-destruct codes in her possession to blow up the stranded Chinese submarine SSN-37-1A.

Detailed walkthrough
There are several ways to start this quest:
 * Travel to the Homestead Motel north of Pilgrim's Landing, enter Room 1D and activate the terminal. Instructions to open a locker near the pier will be received. The key is found inside the suitcase on the bed.
 * Taking the key, opening the locker on the Boardwalk and then taking the Box 1207 - Spy's audio password from the locker will start the quest.
 * Read the spy alert using a terminal in the Administration building of the Turtledove Detention Camp.

Obtain the orders from the locked locker
Once at the locker (located on the right side of the boardwalk coming from the ferry), open it and take the holotape Box 1207 - Spy's audio password. If the terminal in the motel room or the one in the Detention Camp was not read, this will activate the quest. The holotape instructs the Lone Wanderer to go to the bank and use the password on the tape. It also informs them that the safety deposit boxes can only be accessed by the owners' voices.

Access safety deposit box 1207
At the People's Bank of Point Lookout, go to the safety deposit box room and stand in front of the speaker. Activate the holotape received from the locker. The speaker will say "Processing... processing... Safety deposit access granted" upon which box 1207 will open. Pick up the holotape Espionage debriefing. This tape informs you of Agent Jiang's mission to destroy a captured Chinese submarine and his search for another agent, Agent Yang.

Find Agent Yang
Agent Yang has the codes to destroy the sub within a false molar. The molar is found among her remains. Exit the bank, turn right and a few steps eastward will have the Lone Wanderer at the Naval Recruiting Center, which is just beyond the walled bumper car arena. Go through the door behind the counter on the left and activate the DIA Officer's terminal. Access the file "Field Report - Yang Capture/Transfer". Read it to learn the fate of Yang being captured by U.S. officials and detained at Turtledove Detention Camp.

Turtledove is directly north of the recruitment center. The camp is devoid of swampfolk, but swarming with defense robots and ghouls. Enter the morgue through the cellar door, open Yang's remains locker and take the submarine self-destruct codes. Escape the morgue the way it was entered (through the cellar door), or use the hatch located near the cremation chamber, which leads to the septic tunnel. In the tunnel, exit to the east of the Turtledove Detention Camp, in the swamps.

Also, the septic tunnel can be used to enter the morgue circumventing ghouls and sentry bots - investigate the area to the southwest of Turtledove Detention Camp, two or three squares away, while periodically checking the Pip-Boy's local map (as the entrance is not displayed at the world map) near the trash heap. At the entrance to the septic tunnel are two first aid boxes, two ammunition boxes with some shotgun shells, and a yellow maintenance barrier.

Blow up the Chinese submarine
The Chinese spy sub is beached underwater, located south of the Calvert Mansion and near a pair of sunken vessels just west of the lighthouse. Enter the sub through a hatch on the conning tower. Use the terminal in the bow to activate the self-destruct, and flip the failsafe switch in the stern. Before flipping the switch, use Lockpick on a footlocker, which contains several valuable items, including a power fist. The Lone Wanderer will have about 10 seconds to escape after leaving the sub, but until they do leave, nothing will happen.

Not too far from the sub site is a ship far enough away from the blast radius that it can be used as a position to observe the explosion in safety, although it may still be somewhat difficult to see the underwater explosion due to the murky water.

Return to the motel
Head back to the motel, and receive some new orders from the safehouse terminal. The next objective is to meet the head Chinese agent at his bunker, located beside Calvert Mansion, underneath the atrium. The terminal directs the Lone Wanderer to a pair of cryptochromatic spectacles hidden within the toilet tank in the motel.

Head to the bunker
Travel to the Calvert Mansion and enter the remnants of an aviary to the west. Equip the cryptographic spectacles now. The number of rings on each vase represents its number. Activate the vases using the cryptochromatic sequence. The sequence is: 1, 3, 2, 3, 4, 4, 2. A hatch will appear on the floor next to the #2 vase. If entered correctly an audible "5-ping" noise instead of the normal "click" can be heard. If the hatch does not open, enter the code a second time immediately after, ignoring the "wrong" sound effect. After entering the code a second time, the Chinese Intelligence bunker should open.

Escape the Chinese bunker
Inside the bunker is a large number of weapons and ammunition and a workbench. The Lone Wanderer will be approached by a protectron who asks them to leave the hazardous area. Choose to give the robot the pass phrase or tell the "tin man" to get out of the way. There are no benefits or drawbacks to either option save personal preference on where the robot should stand once the quest is complete (assuming it isn't destroyed).
 * If it is chosen to give it the pass phrase, it will escort the Lone Wanderer to a room downstairs for the extraction orders and stand next to that door.
 * Otherwise, simply go downstairs. If left alive without using the pass phrase, the robot will continually guard the door nearest its recharge station and occasionally approach the Lone Wanderer with the option to give it the pass phrase again or use the "tin man" option.

Regardless of the decision, don't go right away. There are numerous crates with various types of ammunition, and a Stealth Boy next to the door that was used to come in. There is also a Stealth Boy and mini nuke on the shelf next to the doorway the protectron either leads the player character through (pass phrase given), or it guards (tin man option given).

Enter the room, and pick up the Backwater rifle on the shelf next to the door, then activate the terminal. The terminal tells the Lone Wanderer the funds for completing the mission have been wired to their next of kin and advises them to take their death honorably. The terminal will then seal the chamber, and fill it with radiation. There are two methods of escape, and one option to buy some time.
 * Scale the nearby lockers and crates to a run-off tunnel visible on the local map.
 * Science (71) - Interact with a fuse box beside the door. It's hidden, poorly, behind some boards leaning against the wall.
 * Repair (30) - Shut off the radiation by closing the floor vent, giving the Lone Wanderer time to think or use the room for storage if they decide to live in the bunker.

Entering the run-off tunnel or escaping through the door will complete the quest.

Reward

 * 350 XP
 * Backwater rifle
 * Cryptochromatic spectacles
 * 8 Chinese assault rifles
 * Copious amounts of ammunition including 5.56mm, 10mm, .44 Magnum, microfusion cells, etc.

Behind the scenes

 * The initial orders found in the hotel room conclude with the line "Zhù ni háoyùn" (in Mandarin Chinese"祝你好運"), which is intended to be Mandarin Chinese for "wish you good luck". However, the correct tones for the phrase are "Zhù nǐ hǎoyùn".
 * One of the terminals quotes the Chinese proverb "世上無難事，只怕有心人" (Shìshàng wú nánshì, zhǐ pà yǒuxīnrén), which generally means "when there is a will, there is a way".
 * Agent Wan Yang's Codename is "Five Claw Dragon." The five claw dragon symbol traditionally appeared on the Chinese Imperial Seal.
 * The title of the quest, The Velvet Curtain, is a reference to "The Iron Curtain", a phrase that represented the secrecy and tight borders that surrounded the former Soviet Union and the Eastern Bloc countries during the Cold War. The East Asian equivalent was known as the "Bamboo Curtain".

Bugs

 * You may not be able to activate the self destruct even if you have the codes in your inventory. Remember that you must enable the self-destruct sequence ON THE TERMINAL before enabling it on the little switch above the goo pile.
 * If you select the first terminal option (the one regarding the mission assignment being in a locker) after self-destructing the submarine, the quest marker for the locker will return despite already having visited the locker. The locker will be empty this time, preventing you from progressing further in the quest.
 * The door leading to the final terminal cannot be opened, pressing the electric switch results in nothing. To fix this, activate the switch using the console.
 * Upon entering room 1D you cannot leave it. The game freezes at the loading screen. To fix this, load an earlier save from outside the room, and then re-enter the room.
 * Attempting to leave the bank may result in the loading screen playing an infinite loop.
 * When getting the password tape, the quest objectives still mark you to get the password from the lockers. You have to first play the "Contact Tape" while still being on the Homestead and then when you finish playing it, get the password.
 * If you are in the Capital Wasteland and you reactivate the quest it will show the quest marker in the Capital Wasteland and not in Point Lookout.
 * Once the quest is complete, going back to the bunker and trying to re-wire the circuit breaker while the door is open results in an instant game freeze. (Fixed in a later patch.)