Anyway. The Underwoods take Billy home. As Mrs. Underwood skips inside to pay the babysitter, Mr. Underwood extricates Billy from the back seat, asking him if he's glad to be home. Billy just stares at him. Mr. Underwood looks freaked out.
In the house, Mr. Underwood is showing Billy all the nifty new stuff they got in the last ten years, while Billy was off somewhere, mysteriously not aging, including his legally younger but biologically older brother, Josh, and their new dog, Sparky. When Mr. Underwood opens the door to let Billy out to play with Josh and Sparky, the dog wigs out, barking hysterically at the younger boy. Mr. Underwood heads Sparky off at the pass, dragging him away from Billy by the collar. Sparky whines piteously, tail between his legs, as Mrs Underwood scurries over to make sure the dog hasn't eaten her son. She coos. Obviously, Billy is evil. Dogs always know these things. Josh gives Billy the stank-eye. Billy stares back calmly.
Back at the hospital/sheriff's station/whatever, Scully tells Doggett that Billy is literally the same boy who disappeared ten years ago. Same blood cell count. Same enzyme levels. Same hormone levels. Same amount of tooth decay. Doggett, of course, wonders how this is possible. Scully reminds him that it is medically impossible. I water my plants, and trim my split ends. Scully tells Doggett that there are cases in the X-Files which explain similar incidents, involving people who were abducted by aliens. Doggett calls that kind of story-telling "lazy." Scully rolls her eyes. Doggett informs her that he's looked into the records of one of the witnesses at the original kidnapping, and that one of them looks pretty fishy. Scully realizes with a very staged gasp that the very records Doggett is referencing are juvenile records, and, as such, allegedly sealed by the court. Doggett doesn't give a shit; he just needs to make the collar! Scully is disgusted. I wonder if anyone has ever actually died from boredom.