The first castle on the site was a timber Motte and Bailey constructed at the end of the 11th century (Approx 1081 when the Normans came to Wales). The original stone building was built in around 1150 and subsequently modified, the tower being added inside existing stone walls at a later date as extra fortification. The Court (manor house building) was started by John Picard in around 1300 but the existing house was built in approximately 1450 by Roger Vaughan. Roger Vaughan was known as the wealthiest 'commoner' in Wales. During the War of the Roses Roger Vaughan changed sides but managed to end up on the Yorkist side, for his help in the war he was Knighted. By the early 15th century, the castle had probably been partially abondoned in favour of the new house. The Court remained the residence of the Vaughan family until 1783 when the building passed out of their hands and became a farm. The vast majority of the paranormal sightings are of a Lady dressed in white with green eyes, mostly in Bedroom 2 opposite the Main Bed Chamber, and she is said to be anxious but not aggressive. Along the Gallery and Battlements a woman in white is also seen pacing up and down and anxiously looking out over as if looking for someone to return. In the Courtroom a little boy has been seen sitting by the door.

The investigation begins with Derek's walk around where he connects with the name Robert Vaughan and Picard as well as a female with green eyes who wore a green dress. In the 1st floor servants quarters he suggests that this would have been used as a court, and although Tretower did host court proceedings they were held on the ground floor. During David Wells' walk around he connected with the spirit of a female who was dressed in white and believed her to be anxious, describing her standing there wringing her hands. The night vigils saw the team split into groups, with Jo, Cath and Rachel investigating the castle keep, where they experienced a few strange noises but nothing more. Meanwhile David and Yvette conducted an Earth Noise experiment, briefly chanting the 'Om' mantra in an attempt to raise spirit activity. At this time it appeared that some strange things took place on the vigils, with Stuart and Karl experiencing a large wooden door appearing to swing open as if by itself, and then closing again. It must be noted that it was very windy outside although they suggested that there were no obvious breezes that could have caused this to happen naturally. Simultaneously Richard was investigating the battlements alone and felt so uneasy that he had to leave. The most significant activity of the night took place in a vigil involving Karl, Stuart, Rachel, Cath where a large flash of light was captured in the ceiling rafters. Meanwhile in the Main Bed Chamber Iain described the sensation of being touched on the shoulder after which David connected with the spirit of a young man who he felt was stood at his side. He revealed that this man was known to Iain and would have been a friend who had recently passed over. The supposed accuracy of the reading did appear to have a significant emotional effect on Iain. Other notable activity included a few odd noises and an instance where Rachel felt ill and appeared to momentarily fall into a trance-like state.