In the chilling premiere episode, the team heads to England to unlock the mysteries behind the grisly 800-year history of Chillingham Castle, widely regarded as the most haunted castle in England. At one time, its dungeons were used as brutal torture chambers that took the lives of countless victims, giving way to a myriad of paranormal claims over the years. The Ghost Hunters International team will sort through these many paranormal accounts and determine what tortured souls still linger at the infamous fortress. From there, the team embarks on a terrifying investigation into the abandoned depths of Mary King's Close in Scotland. This underground phenomenon, a warren of vaults and tunnels, was once teeming with destitute inhabitants at the turn of the 19th century. Now, Mary King's Close is considered one of Scotland's most haunted locales.

In this episode, the team descends into the macabre depths of the Abbey at Lucedio, near Turin, Italy, to unlock the secrets behind the dark legends that make up the Abbey's lurid 1400-year history. Then, a trip to Wales takes them to the legendary Nanteos Mansion, which lore dictates to be the one-time resting place of the Holy Grail. Now, the property is home to numerous paranormal claims, including mysterious music heard in the woods around the house and a phantom horse and carriage that travels about the grounds.

The Ghost Hunters International team heads to an idyllic community in central England to investigate claims at the notorious Belgrave Hall. The nearly 300-year-old house is home to numerous apparitions, including a woman in Victorian clothing whose image was once caught on camera. The Ghost Hunters International team will conduct their own investigation as well as scrutinize the original video recording of this extraordinary event to determine its authenticity. Then, the group travels to Scotland and sets out to uncover the secrets behind claims of restless young spirits at the notoriously haunted Ragged School of Edinburgh, a former residence for impoverished children.

In this episode, the team visits the Elvey Farm Hotel in Pluckley Village, England. Surrounded by 75 acres of countryside, the seemingly quaint locale was home to brutal murders that took place both inside the hotel and in the surrounding woods and its guests and employees alike are now plagued by a slew of inexplicable occurrences, including moving objects and strange sounds and smells.

The team treks high into the mountains of Romania to pay a visit to the Citadel Rasnov, a 13th century fortress that was built to provide protection and defense to the neighboring village below. The castle has been the subject of local legends for years, the most notorious of which tells the tale of two captured soldiers who died in a well on the castle grounds in which they had spent years living as captives. The myriad of paranormal claims made over the years include dark moving figures and unexplainable shadows lurking around the courtyard. The recent discoveries of human bones in both the infamous well and in the castle's basement have given way to yet more sinister tales, making the Citadel Rasnov one of the world's most haunted hotspots.

GHI visits a German fortress whose chambers are haunted by the spirit of a beheaded 13th Century nobleman. Then it's all off to Slovakia, where the team separates legends from facts in the dark halls of Orava Castle.