Dean Koontz in Darkness under the Sun creates a feeling of remorse and guilt with a fear for lacking in understanding or a desire to understand. At the end the protagonist who was not able to help other families but only to save his own creates a desire to act differently and help the other families, while the continuance of crimes similar to the ones that the antagonist had perpetrated create the desire to understand and stop them.
The protagonist is introduced only a small time before the antagonist and they interweave and are exposed at the same time. Foreboding of what will happen, and then a crime and its discovery lead to a realization of an impending danger. The danger is overcome, and a feeling of horror develops that is accentuated through more crimes.
Inaction by the protagonist allows the horror to grow as a crime spree leading to guilt and a desire to understand so such crimes will be stopped.