Guess Who I Saw Today

 is a quest in Fallout: New Vegas.

Detailed walkthrough
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. 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 80 Speech check, Keene can be spoken down (verified). If you give him the specs he'll leave (verified, unknown further consequences). 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, or you can 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 of 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, or you can tell him you think Lily should continue to wear the Mark II prototype.

Whatever decision you choose from above, it will end the quest.

Bugs
When 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.