Presence (short story)

On Christmas Eve 1975, Henry Bergson, while walking down the street in New York City, is being followed by a strange man. Most of the people are running for cover due to the Kellenian invasion overhead, but the strange man approaches Henry and calls him by name. Recognising that Henry is a bum, the man offers him a meal. They talk, and the man, who calls himself the Doctor, learns about Henry's childhood. As a child, Henry was interested in science, and for one Christmas he wanted a chemistry set, but his father didn't believe in him and refused to buy it.

In October 1975, Dr Henry Bergson is being interviewed by a reporter named Hartmann. Henry is reluctant to divulge any information about his classified research on the Kellenians, so instead he tells the reporter a story from his childhood. When he was ten, he wanted a chemistry set, but his parents couldn't afford it. However, a Scottish man, who claimed to have bought two sets by mistake, gave one to Henry's mother to give to him. Then, at university he met a girl called McShane who convinced him to study biology. When she left to go back home to England, Henry was brokenhearted, but made friends with an Englishman named Hex who told him that McShane was dying of a disease that had no cure. This inspired Henry to further his studies in biology.

When Hartmann presses Henry for more information on his classified research, they are interrupted by Hartmann's next interviewee — the Doctor. Henry takes this opportunity to sneak out and headed for a meeting. On the way, he reflects on the fact that Earth is prepared for the upcoming Kellenian invasion.

On Christmas Eve 2005, Ace and Hex skate at Rockefeller Center. They ask the Doctor why they didn't just stop the Kellenians, instead of changing Henry's history. The Doctor describes it as a learning experience, and thinks about where they should go next.