Billy and Nina have no idea how the golden cylinder wound up in their tree fort. They do know they can't open it, although-Billy cuts his hand trying.
Fortunately for Billy, the twins know who can help with Billy's cut: their eccentric friend Doctor Wonky. After healing Billy's hand with his patented Wonky Aid Oil, the good doctor takes a long, hard look at the cylinder. He doesn't like what he sees. The cylinder isn't from Earth and could be very dangerous.
Billy proves Doctor Wonky right when he accidently releases a fairy from the cylinder who traps the twin's mother in a mirror before flying out the window to take over the world.
It's up to Billy, Nina, and Doctor Wonky to stop the wicked fairy, but to do that they'll need magic of their own. Billy will have to collect the bones of a powerful Viking wizard in a different world if he ever wants to free his mother. And to do that, first he has to get there.
Doctor Wonky knows the way. So does the fairy, and she'll do anything to stop Billy and Nina from succeeding.