Ossian is the son of Jack Purdey, a painter; his mother left home when he was nine. Now 16, he and his father are returning to Lychfont House after an absence of seven years. Ossian and his father spent two months there the summer after Ossian's mother left. Ossian made friends with Colin, the son of Catherine Frazer, owner of Lychfont; Colin is two years older than Ossian and was the "sacrificer-in-chief" when they "sacrificed" voles and shrews on the Corn Stone, a large, flat-topped standing stone in a field near Lychfont House.
Ossian and his father are returning to Lychfont House after an 18-month visit to America, where Jack has been painting; Jack is planning to paint a landscape picture based on the landscape around Lychfont House and Jack is to be his model.
As Jack is driving the down a road towards Lychfont House, a large animal that looks vaguely like a pony, with a shaggy head and fetlocks, runs in front of the car, but then Ossian realises that ponies don't have "flame-red eyes and a mouth all dripping crimson". In trying to avoid the animal, the car is flipped off the road, over a ditch and into the same field as the Corn Stone. As it lands, Ossian's forehead smacks into the windscreen and he cuts his head open. Jack is unable to gain control of the car as it hurtles towards the Corn Stone and it appears they will crash into it.
In the meantime, the goddess Sulis' husband-to-be, Ossian, has disappeared and she is forced to call in a scryer to locate Ossian. The scryer discovers that Ossian's spirit has been split into fragments across the centuries. He tells Sulis that she will have to go after Ossian's spirit fragments, but there will be a danger that the barriers between the worlds will be weakened if she behaves in a too-obviously divine manner; at the same time, there is a danger that Sulis will forget her true nature and "turn native" in one of the time periods where Ossian's spirit fragments are, before she can retrieve the fragment. She is only vaguely reassured by the scryer's assurance that Ossian's fragmented spirit will respond to the pull of Sulis' home, Lychfont House, no matter in which century the spirit fragment is residing.
Whilst Sulis is learning this, the 21st century Ossian is getting to know Colin's sister Sue, who has noticed that Ossian attracts ghosts. Then his consciousness slips into the 15th century, and is the apprentice of a goldsmith/alchemist who also has a sideline in torture for the government of the day. We also see through the eyes of the Iron Age son of a priest of Sulis, who is due to become a priest of Sulis himself. And in each age, Sulis is there, trying to capture fragment of Ossian's spirit that is there. Eventually we learn that Jack Purdey did crash his car into the Corn Stone, that Ossian was quite badly injured, and that Colin Frazer doesn't have an older sister named Sue. Finally we learn that Ossian's spirit fragments have all been reunited and he is back with Sulis, and that Ossian will be married to Sulis the next day.
Charles Butler's weaving together of the different Ossian's experiences in the different time zones is skilful and mesmerising; the ending quite surprised me as I had not suspected that Ossian's 21st century girlfriend, Lizzy, was also Sulis, as Sue Frazer and Susannah were in the 21st and the 15th centuries respectively.