(NBC) — Tonight on “Dateline,” when Kelly Horn finds out her father, former FBI agent Scott Horn, has been murdered at his house, she is stunned. As police dig into Scott’s past, they begin to think the key to the mystery might be quite close to home.

In this episode, titled “The House,” Josh Mankiewicz interviews Kelly Horn, Scott Horn’s neighbors and colleagues, Detective Kezzi Henderson, Prosecutor Melissa Hoppmeyer and more, as he tries to unravel the mystery.

Here is a preview of Mankiewicz’s report:

Scott Horn wasn’t the kind of dad to disappear. You see, Scott had spent 23 years as an FBI special agent. Even in retirement, he still scheduled his life like clockwork.

KELLY HORN: If he did something, he normally did that same thing every single day at the same time. he never slept in, either. He was up every morning at 7:30.

Scott’s daughter Kelly was out of the house by 18. Even so, she remembers her dad starting each morning with the same phone call.

JOSH MANKIEWICZ: Your dad called to wake you up every day?

KELLY HORN: Yeah. he would call. (LAUGH) And say, “Are you up?” And then five minutes later, he would call and say, “Are you up?”

JOSH MANKIEWICZ: Oh, so he’s not just the alarm clock. He’s also the snooze alarm.

KELLY HORN: Yeah. (LAUGH)

Except, on that morning —  March 16, 2017 — Kelly’s phone was silent.

KELLY HORN: So I texted him. And, he didn’t respond. And I called him. And, the phone went straight to voicemail. I texted him and I said, “I hope you’re okay.”

JOSH MANKIEWICZ: This is unlike him?

KELLY HORN: Totally.

JOSH MANKIEWICZ: He would respond to you?

KELLY HORN: Yeah.

Kelly reached out to her dad’s next-door neighbors, Marty and Cindy.

CINDY O’DEA: Kelly called and asked me if I’d seen Scott all day. And I said no, I hadn’t.

KELLY HORN: And she said, “Call a wellness check.” So I called the Laurel Police and they came out.

Watch Friday’s “Dateline” tonight at 10 p.m. on NBC4.