The Time Traveler's Wife may be a beloved best-seller, but Rachel McAdams recently told MTV that fans of the book need to prepare themselves for a different version on screen.

“It depends on how attached you get to books,” McAdams said in response to a question about how viewers will feel about the film version. “Because, you know, the films always change [things].”

McAdams stars in The Time Traveler's Wife, which opens on Christmas, opposite Eric Bana. She noted how difficult it can be to squish 400 pages into 90 minutes.

“This film really centers on the love story,” McAdams said of the choices director Robert Schwentke has taken with the film. “The book does as well, but the film is really distilled down to the love story.”

The Time Traveler's Wife is based on the best-selling book by Audrey Niffenegger. The film version will star Eric Bana and Rachel McAdams, both of whom we think are ideal for the roles.

Here's a summary of the movie, followed by a couple still shots from it:

Chicago librarian Henry DeTamble (Bana) has a genetic disorder that causes him to time travel when stressed. Though he disappears often for long periods of time, he tries to build a relationship with artist Clare Abshire (McAdams).

Ron Livingston plays Gomez, the librarian's friend and a liberal attorney who works for nonprofit organizations.