He Came... And Went

He Came... And Went is a side quest in the Fallout: New Vegas add-on Old World Blues.

Quick walkthrough

 * 1) Talk to Dr. Dala about the "other visitor" at the Big MT.
 * 2) Find out the questions the other courier asked Dr. Klein.

Detailed walkthrough
After visiting The Think Tank and talking to Dr. Klein, he will tell you to talk to the other doctors. After talking to Dr. Dala you will learn that another courier traveled to the Big MT and that he was looking for another courier but hadn't found them yet. She can't recall the questions he asked, but hints that Dr. Klein might know.

If you speak to Dr. Klein, he will tell you he asked a dangerous question. Possibly a question too dangerous. Klein said he deleted the memory, but Dala said there might be info written down somewhere.

Evidence of two of the visitors can be found at the Little Yangtze camp (Father Elijah's notes), the Y-17 medical facility (Christine's Report), and the broadcast station (more from Elijah, on the roof). You could also listen to two holotape discussions between the other courier, Ulysses, and Christine in Ulysses' Point.