Nancy Drew, What's That Behind You?

My mother is a huge Nancy Drew fan. When I'm out sourcing Agatha Christie books, I always check for vintage copies of the girl detective. I recently came across this gem.

Judging by the title of the book, one assumes that black blob behind Miss Drew would be a villain wearing a velvet mask. But is it? Here are another couple of possible culprits:

Suspect 1: Nancy Drew's bessie mate Bess Marvin in a berka.

Suspect 2: Ronald McDonald's sidekick with a criminal past, Grimace.

Suspect 3: Barbamama, matriarch of the Barbapapa clan.

Suspect 4: A member of the Black Block, or potentially an undercover cop masquerading as a member of the Black Block.

Suspect 5: Some dude in a terrifying inflatable gimp suit.

(No links for this one kids, this ain't that sort of blog.)

I'm sure that the actual criminal isn't nearly as interesting as any of my suggestions. Probably some mundane petty criminal, or old caretaker in disguise. Or am I thinking of Scooby Doo...