Castle has already revealed a number of spoilers, tidbits and promos for season four. Heck, we've seen a trio of clips from the September 19 return episode.

But might the show's new poster for the new season reveal more than any interview or video already has?

In it, Castle has a mischievous look in his eye, while Beckett has a finger over his lips. Because he might be close to revealing a major secret about the pair? Are they truly just partners... in crime? Hmmm...