The Host by Stephenie Meyer?

Ok so I'm reading The Host and i'm on like chapter 3 or 4...I know that the orriginal font like the one it starts out with is what Wanderer is thinking/saying but who is the other one?? like the one that sneaks into the house....???? I'm really confused and i think i'd understand better if i knew who it was/if it is human/Soul/idk what else!!!!! I really want to love this book like I loved Twilight Series but I need to understand what its talking about!!!!