(Originally published on Oct. 31, 2002) It isn't a dark and stormy night. It's just dark - like most nights.

They aren't prowling a cobwebbed mansion. They're strolling through the well-lighted Woodland Opera House.

And they aren't Ghostbusters. They are Sacramento Paranormal Investigators.

"I am getting the feeling of a male, probably in his early 30s," says Jason

Lindo, pacing the theater balcony. He stops. Strokes his chin. Puts

his hand to his head. "I'm getting a very bad headache over here."

Mark Guilford snaps photos of Lindo, who appears to be standing alone. Guilford's electromagnetic field meter and air temperature gauge don't register anything unusual.

But the men search on. It's just another night in the life of a ghost hunter. And Guilford and Lindo aren't the only ones.

The Sacramento region, perhaps one of the most poltergeist-packed places in the country with its Gold Rush-era ghosts, is one big haunted house for several local spirit-chasing groups and individuals.

They're serious about what they do.

They plod through hundreds of hours of sound recordings and videotape.

They have day jobs. They have families. They wear blue jeans.

And yet, they choose, on their own time, to track down stuff so weird, it may not even exist.

"Right here," says Lindo, 43, on the stairs to the dressing rooms. He moves his hands through the air. "This must be our gentleman."

It could be the firefighter, the one said to haunt the building, the one who died battling a blaze at the theater in 1892. But they aren't assuming.

Lindo, a state-contracted social worker, is the "sensitive" one, describing "impressions" in his mind. Guilford, 33, a Spanish teacher at Laguna Creek High School, is the tech guy, carrying gadgets in his utility vest.

When their readings match up, they have "evidence" - the stuff that ghost hunters are looking for all over the world.

The American Ghost Society, which offers "The Ghost Hunter's Guidebook" for rookies, has 580 dues-paying members. Meanwhile, the International Ghost Hunters Society has trained hundreds through an online home-study program.

Both societies are run by investigators who taught themselves. The drill is ghoulishly simple; anyone can do it: Rule out every normal explanation for something weird, and what's left is, well, paranormal.

After a preliminary investigation, like the one recently in Woodland, ghost hunters will usually come back and stay overnight, bringing high-tech gear such as infrared video cameras, motion detectors and radioactivity meters.

Cameras catch spheres of light - some say dust specks, others say spirits - called orbs.

Tape recorders pick up EVPs ("Electronic Voice Phenomena") - spirit sounds that are heard on tape, not by ear.

Guilford once walked around St. Joseph's Cemetery, on 21st Street in Sacramento, his recorder rolling.

"Does anybody have anything to say?" he queried the air.

"Nope," came the reply when he played it back.

Guilford laughs. But there's also a serious side to the Sherlockian shenanigans.

"The people in houses we're working on right now - these people are very scared," Guilford says. "They don't want it and they don't know how to take care of it."

That's why groups like Sacramento Paranormal Investigators and American Paranormal Investigations, also in Sacramento, offer their services to residents and business owners, free of charge.

Guilford says he gets one or two legitimate requests each month. But investigators get lots more calls and e-mails from people who are a little paranormal themselves.

Even sincere cases can turn out to be bogus. One Sacramento family thought they were being haunted - until they discovered a dog toy was making the mysterious blue marks in the house.

Dennis Hauck, the author of "Haunted Places: The National Directory," likes to work with police officers to ferret out the truth.

"The vast, vast majority of that phenomena is wishful thinking - 'Aunt Nellie's dead and we want her to come back' - or it's a hoax or it's someone misinterpreting phenomena," Hauck says, sitting in his Sacramento home.