A warning given to
Laura Palmer in
Twin Peaks: Fire Walk With Me by the grandson of Mrs. Tremond, after Mrs. Tremond gives Laura a picture to hang on the wall. The
book with the pages torn out is obviously Laura's secret
diary if you've been watching the movie, but the meaning of "the man behind the mask" is as debatable as most of the
Twin Peaks series.
The Fire Walk With Me FAQ at http://www.users.zetnet.co.uk/agill/tp/fwwmfaq.htm contains such speculation as:
"When Mrs. Tremond's grandson tells Laura: 'The man behind the mask is looking for the book
with the pages torn out. He is approaching the hiding place. He is under the fan now.' he's
obviously talking about BOB."
"I'm still not sure if Mrs. Tremond's grandson was saying that BOB is the man behind the mask,
and Leland is the mask; or that Leland is the man behind the mask, and BOB is the mask."