If you know what’s good for you, you’ll listen to Mark Fredrichs.

That’s the moral of the story in the indie-cum-blockbuster horror film “Paranormal Activity.” Micah Sloat, who stars in the cinematic phenomenon, didn’t heed his advice — and look what happened to him.

It’s not good — let’s just leave it at that. Not knowing is half the intrigue of this chilly thriller.

At the eye of the storm is Fredrichs, a Bainbridge Island actor who plays a psychologist, oddly enough, named Mark Fredrichs.

“Actually, I used to be a psychologist,” he said on the phone from Los Angeles.

The role, although not as lucrative as being a psychologist, is worth its weight in gold now for all the publicity surrounding the film.

It started out innocently enough.

After graduating from Bainbridge High School, his daughter, Cali, moved to Los Angeles to pursue a career in modeling and acting. He’s been shuttling back and forth ever since “just to keep the boys at bay.” He offers a graphic image of cockroaches scurrying when a refrigerator door is suddenly opened. “When I come into town, the boys scatter,” he said.

His daughter’s agent asked if he’d be interested in “reading for things” which led to commercials and supporting roles on “The Bold and the Beautiful,” “Lost in TV Guide,” a love story called “Wristcutters” and a few films “still on the shelf.”

In 2006, he auditioned for Oren Peli, who came up with the idea for the movie after hearing noises in the suburban house he shared with then-girlfriend Toni Taylor. He didn’t have a script, as much as a story line.

“It was labor-intensive,” Fredrichs said of the process. “Every scene was shot 50 times.” Afterward, Peli would piece together fragments of takes, trimming seconds here and there to enhance the suspense. The whole thing was in the can for under $15,000.

The film, shot in Peli’s own home in seven days with a Sony HD camera — essentially, a camcorder — has a mock-doc style that adds to the Blair-Witch quality. There are no opening titles and no rolling credits. A time-stamp in the corner of the frame adds authenticity while at the same time signals when the bad things are about to happen, which could be any moment, especially when lovebirds Katie and Micah turn out the lights.

The tension builds as the two become “increasingly disturbed by an unidentifiable presence.”

The couple turns to paranormal psychic Dr. Fredrichs, who outlines the protocol for handling things that go bump in the night. Though Fredrich only appears on screen twice in the movie, his advice is pivotal to the tension. “Listen to what I say,” he implores.

But they don’t.

The audience is drug along for the bone-chilling ride as Micah dismisses every one of Fredrichs’ warnings.

“I’ve gone to a lot of movies,” Fredrichs said, “but I’ve never seen an audience have such a strong reaction. “They’re yelling at the screen, gasping, moaning, ‘Not again.’”

An eery postscript leaves unsettling questions unanswered and the audience mumbling in the aftermath: was that real?

What is unique about this movie, and what landed it on the “Today” show, is the guerilla-tactic marketing that has tweeted the no-budget movie into the Big Leagues.

“What is genius, really, was the idea to sell the movie word-of-mouth,” Frederich said. The “buzz” started as a low drone and has grown to a high-decibel roar.

Paramount, which launched a limited release two weeks ago, agreed to a full release if the fan base reached one million, as measured by the “demand it” button on the movie’s Web site. That happened last week.

By Wednesday, it registered at No. 3 in Yahoo’s box office revenue roundup, grossing a decent $11.5 million. And that is from a mere 160 theaters where the film has been showing, mostly in the cult-status midnight slot. According to the movie’s official Web site, www.paranormalactivity-movie.com, the number of theaters will increase to 800 this weekend and mushroom to 2,000 on Oct. 23.

Even so, Jeff Brein, who co-owns both the Bainbridge Cinemas and The Historic Lynwood Theatre, said that Paramount is releasing the film only to cineplexes with at least 10 screens, leaving Bainbridge in suspense for a few more weeks.

Sadly, residuals were not part of Fredrichs’ contract. But even if fortune is not in the cards, or in this case on the Ouija Board, there’s always fame to fall back on.

“We were at a showing at the Neptune Theater in the University District. When it was over, my daughter stood up and said, ‘That’s my dad.’

He calls it his “Brad Pitt moment” as the mostly college-aged audience rushed him with cell phones flipped open paparazzi-style, wanting to shake his hand, a few asking for an autograph. Not bad for a dad.

And to think he was almost cut from the film.

When Peli took his show on the road for the film-festival circuit, it caught the attention of Dreamworks Studios, which quickly scooped it up (and later transferred it to Paramount). And there it sat, with threats to remake it with box-drawing actors. Peli negotiated that executives had to see the film in a theater before making any changes. When they saw the audience’s reaction, talk of a remake was axed. Even Steven Spielberg reportedly gave it a thumbs up. Well, except for the ending.

“They shot seven new endings,” Fredrichs said. “Even we didn’t know which one they used. I was there. I was in it. But when I saw the movie, it scared the pants off me,” he said.

And if you know what’s good for you, you’ll listen to Dr. Fredrichs.