Punch, or the London Charivari, Vol. 147, October 28, 1914
Chapter 18
In a small room in the same house the detective's daughter methodically pressed her hand against picture after picture hung on the walls. Her face was grimly determined.
At last she was successful. A large section of the wall slid back, revealing a dark opening.
After a few seconds' natural hesitation the brave girl stepped through the aperture.