(I'm reading chapter nine of The Insidious Dr Fu-Manchu. Mysterious events are occurring at Redmoat, the home of Reverend Eltham, formerly Parson Dan, the fighting missionary of Nan-Yang.)
Smith decides that Fu-Manchu must already be inside Redmoat, which Petrie finds fantastic.
As the day draws on, Caesar the dog begins to howl again. Denby, Rev Eltham's nephew, spots something and dives into the shrubbery. There are some shots, then he disappears. They search after him as the light fades and find nothing. Just as they are about to give up Smith goes to look one more time and trips over Denby's body at a spot they've searched several times. Very mysterious!
Smith has a flash of insight. "Heavens! we are fools!" he cries. Well, I wouldn't go quite that far... "LOOSE THE DOG!"
When they do the bells begin ringing and they discover a ladder of bamboo and silk hanging from the fence.
The next day they find the preparations. In the shrubbery a cask has been sunk into the ground and camouflaged with a laurel bush on the lid. Along with the cask, a ladder and hook were provided. Fu-Manchu could enter Redmoat during the day when the gates were open, but could not leave at night when the defences were in place and he would commit his crime*.
What crime? Well Denby has absolutely no memory of events, and probably not because he was hit on the head with a sandbag. He also has "slightly below and to the right of the first cervical curve of the spine ...a minute puncture—undoubtedly caused by a hypodermic syringe." Exactly what and how this amnesiac serum was they don't know. "The nature of the fluid which could produce such mental symptoms was a mystery—a mystery which defied Western science: one of the many strange secrets of Dr. Fu-Manchu." Spooky!
* I'm not totally convinced by this explanation. Why couldn't Fu-Manchu sneak in during the day, catch the Reverend when he's on his own for an hour (writing letters or a sermon or something) do the deed, then sneak out? Still, never mind. That's what Smith claims is the solution.