Could have been SOOOO much better
But still pretty good for a cheap 1970's made for TV movie.
At the time of its broadcast I wasn't even a teenager but I had played around enough houses under construction in our rapidly expanding subdivisions to know that hiding that large a space isn't plausible.
Let alone the missing bathroom.
Old Victorians did have some unique crawl spaces though. Hiding someone in an attic or basement crawlspace makes much more sense along with theuse of a chamber pot when needed.