Now You See Me Now You Don't — Dan Greenburg

A hypnotist's show turns out to be way more than Zack bargains for when he is pulled out of the audience, put into a trance, and his body is "taken over" by the spirit of someone from the past. And that's only the beginning, because the stubborn spirit won't go away when the show's over! It's hard enough having just one self to worry about. What will Zack do with two?