Or could stage some mastermind mystery game. Lock the door and have clues hidden around explaining how they get out. Have two people standing outside the window dressed in really dark outfits and masks (or silly/goofy. Seeing as they won't have their phones or cameras, that means no pics :p). Cut the phone lines. Maybe even leave a video recording for them via Saw style (depending on the theme you go for (dark or silly)

Or simpler, you can create your own story about just how craaaaaazy they got the last night.