Dr. Douglas Monaghan and his his two assistants investigate the case of Carol Fleming, a personal friend of Monaghan's, who sees her double, Helen Reid, at a local museum. The women chat over coffee and learn that they share the same taste in art and are both married to men named Gordon. When they realize that they are the same age and have the same birth date, they realize they must be twins. Monaghan is interested in Carol's dreams where she sees herself and twin girls watching a doll's house burning. He invites Carol and Helen to come to the lab to see if they have a telepathic connection as well and they score an almost unbelievable 100% on the test. After an auto accident in which her husband is killed, Helen moves in with Carol temporarily but but Carol begins to worry when her husband shoes an interest in her identical twin. Carol has her own secrets however and as their relationship deteriorates, so does their telepathic ability.
elen can't understand why Carol would put her ideal home situation in jeopardy by having an affair with Mike and even impersonates her sister to break off the relationship. She's also studying the intricate details of Carol's childhood. When her boyfriend Mike is murdered, Carol has feelings of guilt and Monaghan isn't sure if she might be unstable. As Monaghan's assistants look into Helen's background and childhood, they begin to realize that she is the one who may be seriously disturbed. It becomes obvious that one is setting the other up for Mike's murder and it's left to Monaghan to sort out who is who and who has done what to whom.
Katie Quinn brings her six year old son to the unit when he shows disturbing signs of having lived before.
Having concluded that the George young Joe has been referring to is in fact Georgina McKay who disappeared six years ago, the investigators tell the missing girl's mother about their reincarnation theory. This doesn't sit well with the woman who clings to the hope that her daughter is still alive. As Joe begins to recall more about Georgina's life, the information begins to point to her father as her possible murderer. The police re-open the investigation into the girl's disappearance when they find her body in the loch - exactly where Joe told them to look. However, Dr. Monaghan thinks that Georgina's spirit may in fact be out for revenge.
Yemi is a student who also has to deal with the fact that her father is seriously ill in hospital. Along with her brother Lucas, she spends much of her free time sitting by their father's bedside but the doctors have told to prepare for the worse. Her brother Lucas says he may seek the assistance of someone who know about traditional healers but Yemi dismisses the idea. When Lucas disappears however, she finds an address among his possessions and goes to an old abandoned house where she finds strange markings on the wall, blood on the floor and her brother's name written on a candle. When she returns to the house the next day with the police, something is clearly wrong. The house has now been painted, is furnished and the people there claim they have lived in the property for two years. Unable to explain what may have happened, she approaches Dr. Andrew Gemill for help in understanding what is going on.
Yemi returns to London accompanied by William but she starts to see familiar faces following her and runs off. William and Douglas visit a traditional healer for information. He confirms the rumors that some practitioners of muti, a traditional form of healing, may be using human rather than animal parts, but that's all he knows, rumors. Back at the university meanwhile, Megan starts to receive e-mails from someone warning them all that they are being watched. Douglas makes a connection to a well-healed businessman with connections to Africa and perhaps to Yemi's father.
Findley Morrison seeks Dr. Douglas Monaghan's assistance when strange things happen in his house. All family members, including his wife Carol, son Dominic and daughters Claire and Martha have heard noises, experienced doors opening or closing and perhaps even seen images of someone moving about, though never clearly. Douglas and his assistant Justine McManus spend some time in the house and they too begin to experience some of these strange occurrences. They are also beginning to see the numbers 2976 being repeated. Douglas believes that if there is a poltergeist in the house, it will likely focus its activities on one of the occupants and the evidence begins to point to the Morrisons' eldest daughter Claire. As more information becomes available however and they begin to ask more pointed questions, Carol Morrison abruptly asks them to leave.
Douglas and Justine continue their investigation, even though they were asked to leave the Morrisons house. From the family's reaction, Justine suspects that the strange occurrences may be linked to a Bolivian woman named Lygia who worked as a nanny for the Morrisons some years before, She follows up with Findlay Morrison who says that Lygia returned to Bolivia and has successfully completed law school since. It turns out the Morrisons paid her tuition as well. Douglas still thinks that Claire is the focus of any paranormal activity and decides to test her. As the volume of information continues to grow, Justine finds a vital clue. Douglas was correct in his thinking, only it's someone other than Claire with whom Lygia has made a psychic connection.
Daniel Blakemore seeks out Dr. Douglas Monaghan but has a strange way of doing it - he steps out in front of Monaghan's moving car. He's not hurt seriously however and soon, Monaghan and his team are fascinated by the close mouthed man who clearly appears to have precognitive abilities, that is, the ability to predict future events. Daniel mentions that he was in the military and when he disappears - Douglas suggested he might be suicidal - he and his assistant Craig Stevenson pay a cal on his Regiment. The Chief Medical Officer, Lt. Col. Petra Summers, tells him that Daniel is AWOL and if suffering from trauma as a result of his military service in Bosnia. She would like him to return to continue his treatment but Douglas wonders exactly what may be going on.
Although Daniel Blakemore has died accidentally, the Army still wants to know what the corporal may have told Professor Monaghan and his team. Monaghan himself feels a certain amount of guilt about Daniel's death and is having trouble sleeping. He even imagines seeing him from time to time on the the street or seeing a hooded faceless figure following him. He can't explain what is happening to him. He determines that he's probably being followed and suspects the military of being behind it all.
Douglas Monaghan welcomes back one of his former students, Peter Locke, now a professor who has made quite a name for himself in North America. Craig Stephenson studies the case of John Wade, a self-styled mentalist who has a successful stage show. Although he amazes his audiences, he is clearly using well-worn techniques to correctly guess information of audience members. There are a few anomalies however. Justine McManus meanwhile travels to a psychiatric hospital to investigate the case of a woman who claims she is the survivor of a shipwreck that occurred in 1904 - but only washed ashore in 2004.
John Wade is convinced that he can cure young Chloe Williams of her brain tumor. Craig Stephenson is quite skeptical but newly arrived Peter Locke isn't and is quite keen to study the case. As they learn more about John's background and family history, they realize there may be a more than reasonable explanation for his behavior, though not all can be explained away. Justine McManus goes to Patience Green's home village and finds that it is much as she described it. Her knowledge of the locality and of the people who lived there is astounding but Patience does make one slip that leads Justine to believe there is an explanation for both her condition and her degree of knowledge about the community.
A young couple, Angus and Caroline Jenson, hold a seance to contact their recently-deceased son. Something goes wrong and Angus is thrown against the wall by a powerful spirit. When he starts to experience blackouts and has a vision of a car plunging into the water, he visits the Department of Parapsychology at Clyde for counsel. As he becomes increasingly violent, the team races to determine who or what has possessed him.
Believing that a scarf has set off a premonition of a local woman's death, Justine tries to locate her to prevent the terrifying vision from coming true.
Justine agrees to help one of the students in her tutor group with a research project involving monitoring the girl's boyfriend's sleep patterns. The boyfriend, Stuart, has been suffering from lack of sleep due to terrible nightmares. Stuart's dreams seem to be able to manifest in the physical world, and Justine along with Stuart, his girlfriend Chloe and another friend, begin to experience some unsettling manifestations - including a room full of moths. Dr. Monaghan arrives to help, but the group find themselves trapped in the university. Unable to wake Stuart, they must try to work out what is causing the manifestations before it is too late.
Justine and Craig are hired by Rosie Galt, the manager of an upmarket hotel. She wants them to prove that the hotel is not, as many are beginning to suspect, haunted. The duo are suspect that the job will be a waste of their time, but soon experience strange phenomena: flashing lights, wierd noises, extreme temperature drops and ominous broadcasts on the TV. Could the phenomena be caused by the Rosie's jealous brother, who wants to wrest control of the hotel from his sister, or could they be connected to the newsroom that used to occupy part of the hotel's premises? If it is a genuine haunting, what is behind it?
A young man is approached by lady who predicts his death, handing him a card bearing a drawing of a strange owl-like creature. He approaches the department, but Craig and Justine are sceptical. When he dies soon after his visit, the pair begin an investigation. Justine follows up the drawing, while Craig checks out a business card for an escort agency that was left in the man's jacket. When he tries to log on to the agency's website his computer crashes but shortly afterwards he is approached by a beautiful woman claiming to be from the agency, who begins to seduce him. Although she does not tell him who she is, she is the dead man's fiancee. Meanwhile Justine's investigations suggest that the man's death may have been the work of a succubus - a demon that seduces men to produce more succubi, killing those who do not successfully impregnate them. When Craig is hit by a mystery illness, it appears that he might be the succubus' next victim...
After dabbling in black magic, a young woman manifests extraordinary electrical phenomena. Monaghan and the team find themselves in a race to understand and fight the dark forces attacking her before it is too late. The season finale to series three.
When a young couple, Karen and Ian O'Rourke, move into an old home they discover unique symbols painted on the walls. When they post the image on the Internet, Dr. Douglas Monaghan believes they have found the Tree of Life, a symbol of the Order of the Golden Dawn, a 19th century spiritualist group. At the end of the 19th century Robert Dunbar, a spiritualist, occupied the home and he may have decoded a cipher manuscript that was central to the Order. As Monaghan researches the history of the house he learns that it has a macabre history including the previous owner who was found dead at the bottom of the stairs and Dunbar himself who killed his wife and was hung for it. As Karen begins to see spirits from the past, she desperately wants to leave the house and move on.
As Professor Monaghan continues his research into the house, he finds that there may have been other beliefs at work there and suggests to the O'Rourke's that they leave the house. When they find Rebecca Muir's diary, Monaghan starts to fill the gaps in the history of the house and the Dunbars. What he learns however is that the O'Rourke's may not have acquired the house by chance and that the spirits there have designs on the O'Rourke's themselves.