Ninth Key by Meg Cabot
Suze’s new life in California is looking up. Cool friends, pool parties, good-hair days, and her male room-mate, Jesse, who happens to be a nineteenth-century hottie. But when a screaming, ghostly woman wakes Suze up in the middle of the night, insisting that Suze find someone named Red and tell him he didn't kill her, Suze is none too happy, especially when the ghost disappears before she can get more information. Nonetheless, she asks around to see if anyone knows who this Red person might be and is informed that a local businessman called Thaddeus Beaumont goes by that name.
This is the second book in The Mediator Series.
