A mortal, he was a former CIA operative. Assigned to Prague in 1968, he met and had a moment with Amanda. She was killed and revived in his presence, and hence he was privy to the secret of her immortality.
Years later, living in a retirement community, his son was killed, and he called upon Amanda, convinced that his son's death was no accident but murder. He explained that four scientists, including Charlie's son, were working on a secret project. Three of them had died mysteriously. Amanda agreed to look into it, and in turn asked Nick to do his "cop thing".
When the two men are introduced, Charlie told Nick, "I was you once. I was young."
Amanda and Nick visited the home of the fourth scientist on the team, and discovered that he, too, had been murdered. Another person from Charlie's past, a company man, Martin Foster, tried to cover up the murders and threatened Charlie and his friends.
In the end, Charlie was vindicated, his son's killers exposed.