A Father's Ghost

A geeky young owner of a small Boston electronics store has his life turned upside down when he visits a woman's apartment down the hall in search of food for a stray kitten he has just picked up. The woman's sister embroils him in a vendetta against her father's hate crime murderer and drafts him into her small task force using social networking, the Internet, legal, and "extra-legal" assistance to track and trap a serial rapist who targets single mothers with small children.
Some things are what they seem, and some aren't. The story reads quickly and would be suitable for high school students as well as adults.