Religious belief, the supernatural, deception, family relationships and mental illness are key themes of The Testament of Gideon Mack include .
Throughout the novel a number of strange events and coincidences emphasise the supernatural aspects of Gideon Mack’s story:
Gideon claims to have discovered a huge standing stone in a clearing in Keldo Woods. The stone is not recorded on any maps and suddenly seems to have mysteriously appeared.
It seems that only Gideon is aware of the stone. He is unable to provide evidence of it when his photographs do not develop.
The Devil reveals to Gideon that he placed the stone there for his own amusement as he enjoys
playing with people’s minds
When Harry Caithness and Elsie visit the woods they cannot see the stone. However, Elsie's final confession that she might have seen it leaves a sense of doubt about whether it is real or imagined.
After falling into the Black Jaws, Gideon claims to have been rescued and nursed back to health by the Devil who saved me from the belly of hell
.
The Devil could be a figment of Gideon's imagination but this leaves a number of questions unanswered:
As with the standing stone, whether the Devil is real or not is left up to the reader.
Three witnesses claim to have seen Gideon Mack walking on the slopes of Ben Alder in August 2004, despite the fact that he had died months before.
The two walkers who see him from a distance identify him by his clothes and his limp. He seems to vanish before they catch up with him.
The other witness, Dr Tanner, claims to have spoken to him and positively identifies him from a photo. It is clear that he is certain who he has met from his frightened reaction to the suggestion that he has seen a ghost.