According to the legend told in the Mabinogion, he is kidnapped from his mother Modron (who is an incarnation of the Mother Goddess) when he is only three nights old. Taken to a place nobody knows about, no one knows anything about his abduction, not even whether he is dead or alive. In the tale telling the story of Culhwch's quest to win his beloved Olwen, Culhwch engages in a series of trials. Each one of them enables him to succeed in the next one. One of these trials consists in finding Mabon. Culhwch has to release him from his prison but before he can do that, he first has to find information that will reveal to him where Mabon is held captive. In this quest, King Arthur offers his help to Culhwch and takes his knights with him. Culhwch and his companions investigate by questioning several animals, but none of them knows where Mabon is nor whether he is dead or alive. Each creature directs them to an animal that is older than them and who might have heard something that could help them. As a matter of fact, Mabon is the oldest man on earth for he was there before anybody else. As the story goes on, the only animal who may know what happened to him is the Salmon of Llyn Llyw, who happens to be the oldest animal on earth. The companions find him and he leads them to the prison where Mabon is held, which is identified as Gloucester. At the foot of the prison, Culhwch and his fellows hear lamentations. When they ask who is crying so hard, Mabon names himself. The companions engage a fight and release him.
Symbolically, Mabon was born twice: the first time from his mother Modron, and the second time with his release by Culhwch. Though he is a god, he helps the humans with whom he has peaceful relationships. He thus belongs to both worlds (divine and human), which reflects what happens at the autumn equinox for which he recently became a symbol. Representing light, Mabon is indeed kidnapped and held captive in a prison underground, that is to say in the darkness. Here as well as at the equinox, darkness is victorious over light.
During his long detention, Mabon is held in a prison underground and thus in the dark, in which he is forced to live and which he has to accept. This introspective spread was designed especially for the autumn equinox and invites the Querent to explore his own part of darkness so as to release himself from the prison built by his fear of it.