(NBC News) — On Friday’s “Dateline,” a Southern California woman’s fall down the stairs initially appears to be a fatal accident, but investigators help to unravel Susann Sills’s husband’s story.

Here is a preview of Keith Morrison’s report:

If these walls could talk, oh the story they would tell.

Dr. Sills was in a life-and-death battle. Only this time the patient was his wife Susann.

Minutes into the call help arrived. But it was too late.

ERIC HATCH: Susann was lying on her back with a blanket covering her body.

A mysterious fall down the stairs in the middle of the night.

THERESA NEUBAUER: A fall? She never fell.

Susann’s mother veered from disbelief to acceptance and back again.

KEITH MORRISON: It was eating at you.

THERESA: Yeah. Niggling at you. Just there all the time.

Nothing made sense to her family.

FRANK GAULDEN: I just couldn’t believe that it was just over like that.

What a sudden and strange way for her to die.

PETER ARSUAGA: I mean, this was really odd.

THERESA: Had to be something sudden, something unexpected.

Just how unexpected, they had no idea.

Watch “Dateline: If These Walls Could Talk,” Friday on NBC4 at 9 p.m.