Guess Who I Saw Today

Guess Who I Saw Today is a side quest in Fallout: New Vegas.

Detailed walkthrough
To begin the quest, the Courier must go to the Jacobstown lodge and talk to Doctor Henry and tell him they will help him research why the local night stalkers have begun turning invisible.

Meet with Lily Bowen, a nightkin standing by the pen outside the front of the lodge, after accepting the quest. One can invite her to come along, but it's not required (this will only work if the player does not have a fellow humanoid companion already).

Exit Jacobstown and circle around to the northwest to locate Charleston Cave, and enter. Continue through the cave. Eventually, one will come across a couple of bighorner bodies and a nightkin body, with Oh, Baby! next to it. Examine the nightkin and take his chewed Stealth Boy, the player will then be prompted to return to Doctor Henry back in the Jacobstown lodge. The night stalkers will not attack if the player has the Animal Friend perk.

Talk to the doctor back at Jacobstown. He'll inform the Courier that since the chewed Stealth Boy was a dead-end, using the Mark II Stealth Boy is the only remaining line of research available to him, and Lily is his best experimental subject. Talk to both the doctor and Lily; they both will agree to the experiment. It's a success, but as soon as the doctor is finished, Keene enters the room and demands the Stealth Boy Mk. II specs.

Note: If one talks to Lily while they are away from Jacobstown, she will run back to Jacobstown. If one needs her, they should be mindful of where this conversation takes place.

Make sure Doctor Henry actually does the experiment; it should not take more than 30 seconds for him to start.
 * Passing a Speech check (80) will cause Keene to back down.
 * Giving him the specs will cause him to leave peacefully.
 * If the specs aren't handed over, he and the two other nightkin will attack.
 * One can easily draw the three of them outside and let the super mutants help with the fight.
 * One can also go in the corner (where the wheeled tables are) to prevent the nightkin from attacking (or delaying them).
 * It is possible to use a Stealth Boy and reverse pickpocket a C4 plastic explosive onto Keene and his 2 nightkin before speaking with him. This way, if one chooses to fight them, a detonator can be used to kill all 3 at once.
 * Lily will leave the lodge as Keene is coming into the room, and will not help with the fight.

Speak with Doctor Henry again.
 * Passing a Science check (90) will convince Henry to test the Stealth Boys on night stalker brains.
 * One can also inform the Doctor the risk is too great, and Lily should not wear it.
 * One can also tell him that Lily should continue to wear the Mark II prototype.

Whichever decision is chosen, it will end the quest. It is not confirmed if different decisions have any effect on game-play, though Lily will always be able to be taken as a companion. Passing the Science check gives 590 XP, 90 more experience than the other two options do.

Regardless of the outcome, the player will NOT be able to acquire the Stealth Boy mark II prototype.

Behind the scenes
"Guess Who I Saw Today" was a soft jazz song written by Murray Grand and performed by Elisse Boyd.

Bugs

 * Immediately after using the speech option with Keene telling Doctor Henry to do as he says, there will be a black screen crash.
 * Sometimes, if you beat Lily to the lodge trying to exit the building again will cause a black screen crash. There is no fix for this at this time aside from exiting the game, erasing all add-on content (including patches) and loading the game with out the add-ons.
 * If you come back to the lodge while the quest "Eureka!" is active, Doctor Henry may not respond to you talking to him, resulting in it being impossible to finish the quest.
 * If you go into V.A.T.S. on Lily while she is testing the Stealth Boy MK II and she is invisible she will turn visible. However, this will not affect the quest.
 * If you ask Lily to help Doctor Henry while she is waiting in the Presidential Suite of the Lucky 38 without asking her to come with you, she will immediately leave to go speak to Doctor Henry. When you return to Jacobstown Lily will not be present anywhere, but you can stil talk to Doctor Henry to initiate the quest. He will go through the dialogue one sentence at a time, and the only solution to get the quest finished is to leave the building and return to Doctor Henry after each line. Please note that this solution does not work on Xbox 360 and PC. This may be fixed on the PC by using console commands.
 * If you have already stealth killed the two other Nightkin that follow Keene (even if nobody saw you do it) Doctor Henry and Calamity will suddenly become hostile upon Keene entering the room without his buddies, instantly failing the quest (being out of sight and/or Hidden will not prevent the Doctor and Calamity from becoming hostile).

Nachtpirscher, ick hör dir trapsen ¿Sabes a quién he visto? Догадайся, кого я видел! Здогадайся, кого я бачив!