Ghosts of Eden by Keith Deininger

This is the story of Kayla and Garty. Kayla comes from an abusive, neglectful family and Garty is a hopeless drug addict. Unbeknownst to themselves they are brother and sister, and have been sent to stay with their strange and enigmatic Uncle Xander. Their Uncle believes that Kayla has powers and Garty is there to be his assistant. They both have no idea though that Xander has other, nefarious plans...

This was really, really trippy! There were several threads and realities converging on each other and at first it was difficult to work out what went where, but once I had a handle on where the story was going, I had an absolute blast reading it. I loved the characters, and the 'otherworldliness' lent an interesting twist to the story.