After the events of Scanners 2, Kellum went deep undercover to protect his older sister and himself from being exploited by government agencies. A couple months later, his girlfriend has a freak-out and leaves him, taking their dog (Trooper) with her. Kellum finds that his parents had another child, Jeannie, before they were killed. They had left her with more friends that eventually accept David into their family so he can be with Jeannie when he realizes she is a scanner, but has a much weaker ability compared to David's. In effect, he becomes Rodney McKay and goes back to school after he masters his abilities and is able to function in high population areas without being stressed. As McKay, he does get his multiple PhDs and is hired as a civilian contractor with the US military and eventually goes to Atlantis. Events on an away mission force McKay to reveal that he's a Scanner, but his identity holds as Meredith Rodney McKay. Sheppard has some difficulties with the fact that McKay has psionic abilities but they do get together (please, must have a hot sex scene with Rodney as bottom). The SGC may look into McKay's background and may/or may not find his true identity-depends on the author's discretion. Also, McKay's abilities have grown over the years, so he's pretty damn powerful. The Ancients can't sense them, since McKay hides his ability extremely well but they may make an appearance since McKay revealed his abilities on that away mission to save his team. Must have a happy ending, I get depressed on sad endings.