Frankie and Lulu both need a vessel to possess to enjoy being alive together and get married.

Frankie: Honey who would you like to possess?

Lulu: Baby who would you like to possess, I don’t care who I possess as long as they’re hot and I can leech of their life’s work, so perhaps a celebrity or a rich person or something like that.

Frankie: What about…

You stumble upon the spirits while they’re deciding what to do.