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Foster is the man who saves Liam, Maddy and Sal from their deaths. He takes them to their field office, introduces them to their new jobs and takes them to an assassination of John F. Kennedy to see if they can spot the shift. He only delays the assassination. He stays during the apocalypse and then leaves. He tells Maddy about Liam aging everytime he travels in time. In Day of the Predator Maddy finds him in Central Park and he reveals that he is, actually, Liam O'Connor after he ages from time travel. He is about to die from tachyon particles damaging the cells in his body. He and Maddy regularly chat during the rest of the books in central park but because he will be in the same time, he can never remember that they have had a conversation although he is astute enough to pick up on what is happening due to his own experiences.
He is shot and killed by the support unit called Faith in The City of Shadows.