Sea of Souls follows para-psychologist Monaghan and his two sidekicks from a fictitious Scottish University that investigates paranormal activity.
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.
Helen 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.
Monaghan and his assistants investigate paranormal phenomena, specifically the transference of souls from the dead to the living or, more simply, reincarnation. After an unsuccessful trip to Lebanon where a young boy apparently had detailed memories of another life, they're faced with the case of 6-year-old Joe Quinn who starts to have memories of another life belonging to someone named George: a home by a lake; that his "other mummy" had red hair; and of a drowning. Is he however remembering a past life?
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.
