(NBC News) — Friday on an all-new two-hour “Dateline,” a private investigator looking into a decade-old case about a mother of four who vanished uncovers clues that turn a town upside down.

Here is a preview of Keith Morrison’s report:

It was Oct. 29, two nights before Halloween, when they gathered in their costumes and masks. To hide their secrets? Perhaps?

Including a woman named Karen Swift — life of the party, usually.

JENNY GURIEN: She said she wasn’t having a good time.

After midnight, Karen got a call from her nine-year-old daughter Ashley.

ASHLEY SWIFT: I was at a friend’s house, and I wanted to come home.

David Swift stayed up to make sure they got home safely, but when he woke up the next morning, Karen was gone.

JANICE BROACH: It was a very strange missing persons case.

The mystery of what happened to Karen Swift was becoming bigger than anything this town had seen.

HEATHER COHEN: I came in and I stirred up the hornet’s nest.

JANICE BROACH: Stories started coming out about how she was hanging around with really wild crowds.

KEITH MORRISON: Strange bedfellows?

HEATHER COHEN: You could say that.

Oh boy.

Watch the all-new two-hour mystery, “Dateline: After the Halloween Party” airing Friday at 9 p.m. on NBC4.