After a cheerleader is murdered, her boyfriend discovers that she is a ghost and ends up falling in love with her twin sister who happens to be a serial killer.

I changed the ghost to a she.

No, the girlfriend is.

She gets murdered but he is a ghost? I'm making an assumption that the cheerleader is a girl.?

"turns upside down" is such a generic statement. Give us more specifics.

So... his girlfriend gets murdered, but he is a ghost who dates his girlfriend's twin sister who is a serial killer? If he's not a ghost it makes a lot more sense to me...

I'm not going to lie, whichever I try and decipher this, I can't figure out what's actually going on or why.