The Fall to Domum, Castle, Book 1

Jon McKinney is anything but an ordinary Boston university student on the path toward a career in computer science, but he's spent his life feeling like he should be more than he is. When he inherits a castle in Ireland from his presumably drowned Uncle Gordon, he leaves behind his education and his girlfriend to see what awaits him on the other side of the world. Once there, he meets the fascinating and beautiful Liz O'Doul and discovers a strange crystal he mistakenly believes is merely a good luck charm. Liz tells him Miller Castle has a long and colourful history of strange creatures lurking about its stone walls, but Jon doesn't believe it...until Liz catches a dwarf named Gilbert trying to steal unmentionables from her suitcase. Jon pursues the creature up the steep staircases of the castle. But, just as he catches Gilbert, the two of them tumble out the window and through a magical gateway.