I am not a fast reader. So the fact that I finished all five books in David Downing's John Russell series in just over three weeks means that a) Zoo Station (book one) hooked me on the first page b) I made more time to read fiction that at any point in the past five years of get up-research-write-parent-go to bed-repeat c) Downing is a master of plot, characterisation and pace.
The word penumbra is often rendered "half-light." The Latin origin paene umbra literally means "almost shadow." In between the shadow and the light there is a zone through which we may see what is in the penumbra, but we see it with this darkened hue, and it is problematic to say whether it is illuminated or not.