It's a bitterly cold spring evening and the sun is beginning to set over Culzean Castle on the Ayrshire coast.

Inside, away from the chilly night air, a small group is gathered in the main lobby busying itself with a complicated-looking collection of electrical equipment. On a table is a pile of assorted batteries, an undoubted necessity given the number of camcorders, cameras and digital recorders scattered around the room. In the corner sits a large microphone-cum-satellite dish. It all looks a little too high-tech to be the monthly meeting of the local Woman's Guild.

In fact, all this equipment belongs to the Ghost Finders, a team of amateur paranormal investigators whose aim is to uncover the truth about Scotland's most haunted sites. The group was set up 12 months ago by Mark Turner, his girlfriend Lisa Lundie and her sister Joanne.

Sharing a long-running interest in the supernatural, the trio, based in Cumbernauld, decided to formalise their interest by conducting their own investigations. Their team, which has since swelled to 11 members, has already visited a series of "haunted" locations around the country including Culcreuch Castle in Fintry, Hopetoun House in South Queensferry, and the Museum of Transport in Glasgow.

Tonight, though, it is the spectres of Culzean Castle who will take centre stage. Perhaps.

The Ghost Finders' investigation follows a rigid pattern. First comes a thorough briefing of the rules: no-one to wander off on their own, no whispering, and most definitely no wearing of waterproof clothing indoors. The latter, it transpires, is for technical rather than fashion reasons: there are concerns the rustling fabric could be mistaken for ghostly activity.

When it comes to things that go bump in the night, this group take the job more seriously than Scooby-Doo and the gang ever did.

Formalities out of the way, it is time to begin the investigation with a "walk-through" of the castle. The team members are led by Scott Williams, a medium . . . who, they insist, wasn't told in advance where he'd be going, making research impossible. The group trail behind in ones and twos, some filming the proceedings on camcorders, others snapping random pictures of the rooms on digital cameras. They are hoping to capture "orbs" . . . white, or occasionally coloured, balls of light which are said to signal paranormal activity. These, explains Turner, are not visible to the naked eye, hence the need to record them electronically.

Motion sensors, infrared thermometers, cameras, camcorders and EMF meters are also being pressed into use. The latter are used to measure electro-magnetic fields, another factor believed to indicate paranormal activity. Most interesting, though, is the group's use of EVP voice recorders (which look suspiciously like any other digital voice recorder).

EVP . . . which stands for Electronic Voice Phenomena . . . was at the heart of the recent Michael Keaton horror flick, White Noise. In simple terms, EVP is what paranormal investigators believe to be spirit voices. This voice or sound is not generally heard at the time of recording; instead it appears to have been imprinted directly onto the tape or digital recorder. That's the theory, at any rate.

As locations go, Culzean Castle, which dates back to 1165, has no shortage of spooky nooks and crannies. As the group make their way through the labyrinth of high-ceilinged rooms, Scott Williams describes his visions. In one room he picks up the presence of a family; in another, at the top of a staircase, that of a solitary man . . . who, he adds pointedly, is watching.

The plan is to start with a seance in the State Room, but first the team need to set up a "lock-off" in the Earl's Bedroom, apparently the most "active" of all the rooms. Four cameras . . . all with night-vision . . . are left in the dark, and a series of digital recorders are set to voice-activated-recording mode. The lockoff is meant to rule out any external intervening factors. Before leaving the room, Turner booms: "Is there anyone in here who would like to communicate with us? We're leaving equipment for you to do that." Disappointingly, but perhaps understandably, there is no immediate reply.

The group move to the opposite side of the castle for an hour-long seance, during which nobody appears to leave the room. The castle's night manager, scrutinising proceedings and the surrounding area on CCTV . . . with a lot of priceless artefacts lying around, he doesn't want anything nicked . . . later confirms as much. Emerging from the room, the team claim to have gathered some EVP recordings, including one in which a male voice appears to be shouting "you f, , ing bastard". Uncouth types, these restless spirits.

A palpable ripple of excitement runs through the group as the tape is replayed, but the hunters are maybe a little unnerved too.

Turner, a 30-year-old web designer, is man enough to confess to the occasional attack of the heebie-jeebies, but says he tries not to let it interfere with the task at hand. "At the end of the day we're here to get evidence, and if every time anything happened in the dark we ran away, we wouldn't get very far."

Afterwards, everybody returns to the Earl's Bedroom . . . the site of the lock-off . . . where Turner picks up one of the digital recorders and hits play. Astonishingly, there is a series of sound-activated recordings, which sound uncannily like screams and angry hisses.

Not everyone is convinced by such evidence:

Dr Caroline Watt, acting head of the Koestler Parapsychology Unit at the University of Edinburgh, for one. She is sceptical about the whole notion of EVP. "Our brains are very good at recognising or identifying patterns where none might actually be there, " she explains. "It's a bit like seeing faces in clouds. The same goes with recognising random sounds. In a noisy environment, such as when we're vacuuming or in the shower, the brain interprets these noises into a pattern. For example, you could imagine that you hear the phone ringing or someone calling your name. It's the same sort of phenomenon."

Naturally, the Ghost Finders don't share Dr Watt's scepticism. But you do wonder what makes a group of professional people run around ancient buildings in the dark hoping to run into a spook or two.

Each member of the group has their own reasons. "Nick" . . . he won't give his full name for fear of upsetting his employers . . . first became interested in the paranormal following a near-death experience at an antiVietnam demonstration in London back in 1968. He was part of a crowd of protesters trying to pass a police barricade at the US Embassy when someone tripped, sparking a tumble of bodies. Nick found himself at the bottom of the pile.

"I couldn't move and I started panicking, " he recalls. "Then the realisation set in that I was going to die, and I felt quite calm at that point. The next thing I remember I was being drawn up a tunnel towards a bright light. I was aware of a loud swishing noise. I was in a horizontal position and there were three females waiting there for me. I remember feeling desperate to get to them. Then the sound slowed down, like a record stopping, and I was drawn back into my body. I have no idea how long I was out for. I had a few cuts and bruises and had lost my shoes, but otherwise I was physically okay."

Nick, 40, is now the team expert on EVP.

"The first voice I ever got, I was terrified, " he says. "I actually heard the voice as it came through. There was a click, like someone snapping their fingers, high above my head. Then I played back the recorder and it was a young boy saying, I'm here.' It's a moment I'll never forget. It's like catching your first fish or winning your first race." Like many of the group, Nick dreams of catching a full materialisation of a ghost on film. "I've seen what I believe to be the ghost of a cat, " he offers.

Other members of the team have equally personal reasons for being here. Thomas McDonald and Lorna Prentice, both from Cumbernauld, are relative rookies in the ghosthunting business: Culzean Castle is just their second investigation. McDonald already has his own theories that ghosts could be much more than simply spirits of the dead. "It could also be explained as a time slip, " he says. "Or if someone has died unexpectedly, the stone or fabric of a building could hold on to that energy."

The 33-year-old surveyor and his 35-yearold girlfriend, a nurse, are also keen to test the theory of life after death. "I'm not convinced it's the religious idea of heaven and hell, but I believe there is something else beyond death, " says McDonald. "I'm doing this for my mum and dad, who have both passed away within the last few years. I'd like to know that when I close my eyes for the last time I'll be able to see all the people I miss again." His eyes are wide with belief. "I'm going to keep doing this for however long it takes to get an answer."

Six weeks later the Ghost Finders meet again, this time at Inveraray Jail in Argyll, a former prison dating back to the 19th century. Turner visited the site two weeks previously with an English paranormal investigation team. On that occasion, he says, he began to feel ill when he entered one of the old cells.

"I was really dizzy, and it felt like I couldn't feel the floor underneath me, " he says. But he is determined to brave it again.

Today's investigation follows the established format: a briefing followed by a walk-through of the buildings. When it comes to the room in question . . . cell number six . . . Turner doesn't falter, marching straight in. Less than 30 seconds later, however, the smile falls from his lips and he starts to sway, clutching his head.

He stumbles outside and crouches on the ground, ashen-faced. "My head is spinning, " he says. "It's horrible. I feel like I can't control it." He stretches out an arm, his hand visibly shaking. "I didn't think it would happen again.

I can't believe it."

Whether his reaction is physical or psychological, he is nevertheless clearly shaken by the experience. Afterwards, as the rest of the group finish the walk-through, he sits in the kitchen quietly sipping sweet tea. "I still don't feel right, " he says. "It was such an awful feeling, quite scary. My head was swirling and my body started to shake. I couldn't control it. It came on really quickly, this intense sensation."

Turner's experience, however, turns out to be the highlight of the Ghost Finders' night at Inverary jail. The motion sensors are set off twice, but on neither occasion does anyone manage to find what was responsible. "Once we were off on a break, and the second time we'd just got to the bottom of the stairs on the way to having a break when we heard them go off on the floor above, " says Turner. "They were toying with us."

"For me it felt a little flat, " admits John Lundie, the self-described sceptic of the group. "It is a historical site, but I didn't feel anything spooky about it." The 49-year-old mechanic, who is the father of founder members Joanne and Lisa, was asked to join because he firmly doesn't believe in ghosts.

"They want me to come along to the investigations to see if I can find other reasons, perhaps more rational ones, for some of the things that happen, " he says. "Sometimes they get a bit too excited, particularly when it comes to orbs. I mean, we don't really know for sure what an orb is. It could be anything . . .

dust, maybe, or insects."

Lundie does admit to feeling frightened on occasion, but doesn't think there's anything particularly paranormal about that. "It's natural to feel afraid when you're on your own anywhere, " he says. "It doesn't mean there's anything else there that's scaring you."

Dr Watt of the Koestler Unit agrees that excitement can be a big factor in the whole ghost-spotting business. "There are lots of normal psychological processes that are going on when people have experiences they interpret as ghostly, " she explains. "If someone already believes in ghosts and has an expectation that the area in which they are going to be might be haunted, they are more likely to interpret seeing a shadow or a shape, or feeling a draught, as being due to a ghost.

Those who don't believe, however, may have exactly the same experiences, but they will put a different label or interpretation on it."

Some people might also simply be more sensitive to their environment and so more likely to pick up on factors such as visual or temperature changes. "There is also a theory that people are responding to infrasound, " says Dr Watt. "These are very low-frequency sound waves and there is some evidence that infrasound can make one feel very uneasy and induce blurred vision, giving you strange, fearful sensations. It's been suggested that some haunted' locations contain infrasound, and so people may be responding to that."

Still, for all her rational explanation, Dr Watt is determined to maintain an open mind. "I'm a scientist, and so I would never say something is impossible, " she says.

Proving the impossible possible is the Ghost Finders' very reason for existence. "I want verification, " says Mark Turner. "If we knew 100 per cent that they were there, it could open so many doors for everyone . . . and take away so many fears. Mourning the loss of a loved one? That could go. It could disappear just by knowing that life after death existed. At the moment it is a very large untapped area. And we intend to tap it."

For more information on the Ghost Finders, visit www. ghostfinders. co. uk