In Boy X by Dan Smith, young Ash wakes up in a strange place with no idea how he got there. (Yes, this is middle grade fiction, not a twenty-something documentary.) By "strange place," I mean "strange medical place." He appears to be alone there. No mother! No one else, either. He stumbles outside where he finds a girl whose father works in the facility he just left. She informs him that he is on an island in Costa Rica. And he's been there for two days. The last he knew, he was in New Jersey. So, man, what's happening?)
Within minutes an alarm goes off! Men are running! Oh, gunshots! A helicopter is shot down! And Ash can feel himself changing.
The two kids end up having to save their parents (because Ash's mom is there, after all) and pretty much the world. What makes this believable is that changing Ash is doing. Sure it's far fetched in our world, but it's what makes what's happening in the world of the book work.
A real kid thriller.