The disappearance of a teenage boy in Chicago sends investigators to the home of contractor John Wayne Gacy; a team of officers track his every move until a chance encounter leads to a horrifying discovery in the crawl space of Gacy's home.

An examination of Gacy's past reveals unsettling evidence that authorities knew he was a sexual predator; still, Gacy was able to evade law enforcement for more than a decade as he committed his deadly crimes.

A quick verdict doesn't end the story; the specter of more victims has investigators digging again.

Questions about the Gacy case linger 40 years later, as does the fallout from his terrible crimes.