Books like The Demon's Den
Carolyn Keene
The Demon's Den is 200 pages, about 3 hours 40 minutes at 250 words a minute.
6 books to read next
How long each takes
A Matter of Choice 4.7 h 
Mad House 1.8 h 
High Stakes 4.1 h 
The Ocean of Osyria 1.8 h 
The Deadliest Stunt 2.1 h 
The Hardy Boys and Nancy Drew Meet Dracula 2.9 h Bar height shows length. Estimated at 250 words a minute.