The Dragon and the Fairie - The Vasara Chronicles, #1

Sixteen-year-old Andy has an appetite for adventure, so when he stumbles upon a ruined, condemned castle perched on a remote island in the Hudson River, he can't resist the urge to explore it. Together with his reluctant sister, Emilia, they discover that the castle has housed a dark secret for centuries-a gateway to a world inhabited by dragons, wizards, faeries, and demons. When they pierce the barrier between the world they know, and this other world, their crossing sets off a dark chain of events: Emilia vanishes during the turbulent crossing, and Andy lands in a castle governed by Devon, an evil wizard.
Forced to embark on a journey filled with dangers he can't foresee, a love he doesn't understand, and entangled in a prophecy that could very well end life as he knows it, Andy must find a way to survive the new world he's in, rescue his sister, and fulfill his destiny. But can Andy and Emilia understand who they really are in time, or will they lose everything?