Guess Who I Saw Today

 is a quest in Fallout: New Vegas.

Quick walkthrough

 * 1) Go to Jacobstown.
 * 2) Speak with Doctor Henry.
 * 3) Head to Charleston Cave.
 * 4) Retrieve the Chewed Stealthboy.
 * 5) Return to Doctor Henry.
 * 6) Talk to Lily Bowen.
 * 7) Deal with Keene.

Detailed walkthrough
To begin the quest you must go to the Jacobstown Lodge and talk to Doctor Henry and tell him you will help him with a problem.

Meet with Lily, a smaller Nightkin standing by the pen outside the front of the lodge after accepting the quest. Invite her to come with you. (This will only work if you do not have a fellow humanoid companion already) (Optional).

Exit Jacobstown and circle around to the Northwest to locate Charleston Cave, and enter. Continue through the cave following your compass (generally moving downhill) while dispatching Nightstalkers and eventually you'll come across a couple of Bighorner bodies and a Nightkin body, with Oh, Baby! next to it. Examine the Nightkin and take his Chewed Stealthboy and you'll be prompted to return to the Doctor Henry back in the Jacobstown lodge.

Back at Jacobstown, talk to the doctor. He'll inform you that the Chewed Stealthboy may be a breakthrough in his research and that 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 work done.

If you can pass a speech check (80), Keene can be spoken down.
 * If you give him the specs he'll leave.
 * If you don't give him the specs, he and two other Nightkin will attack.
 * You can easily draw the three of them outside and let the Super Mutants help you do your work.
 * You can also go in the corner (where the wheeled tables are) to prevent the Nightkin from attacking you (or delaying them).

In the lodge, speak with Doctor Henry again.
 * If you can pass a science check (90) you can convince Henry to test the Stealthboys on Nightstalker brains.
 * You can also inform the Doctor the risk is too great, and Lily should not wear it.
 * You can also tell him you think Lily should continue to wear the Mark II prototype.

Whichever decision you choose, it will end the quest. The outcome of each decision seems to have another effect on the game.

Bugs
If you kill Calamity before letting Doctor Henry experiment with Lily Bowen then the quest will be stuck and you cannot finish it.

If you enter the lodge after talking to Lily and then initiate the test before she enters, she will either remain outside, invisible, or she will run over to Doctor Henry and neither of them will talk to you when prompted. This may be fixed by pick pocketing Doctor Henry.(Doesn't always work).

If Lily has been taken on as a companion, it is possible that she is automatically dismissed at the conclusion of this quest, and must be re-hired if she is to continue travelling with the player. (Confirmed Xbox 360, PC)

After you give Doctor Henry the chewed stealth boy he will not experiment with Lily and the quest will be stuck. (so will the quest For Auld Lang Syne as you will not be able to recruit Doctor Henry)

Lily will continue to say that she is helping Doctor Henry and neither will allow you to progress. This can be fixed by killing Lily as she stands against the wall (she won't attack), and then approaching Doctor Henry, in which he will give you his pass-phrase for the "For Auld Lang Syne" mission. This will disrupt the "Guess Who I Saw Today" mission, but seems to be the only alternative in this instance.