Mother usually paints outdoors, and father goes boating, or both travel out of town. Withers and his sister, who are agents of the Dark, desperate to stop them at any cost. So begins their quest for the Grail on behalf of the Light, which they have to achieve while being harried by Mr. He explains that some British artefact may have been hidden here long ago, and confirms that they will have dangerous grown-up rivals in its pursuit. Up on the headland they show him the map, and he tells them that it is a copy of an even older map that shows the way to a hidden treasure and that the children are now in great danger. The children decide that it is time to confide in Great-Uncle Merry. Soon the house is burgled, with attention paid only to the bookshelves and the wall hangings, and the children guess that someone else knows of and seeks the manuscript. He asks some probing questions that arouse Jane's suspicions and she decides to return home. The man at the vicarage is not the writer of the guidebook, but he offers to help Jane. She realises that the map in the guidebook is similar to the secret map, but also different somehow, so she decides to visit the vicar.

While Jane is alone in the Grey House she finds a guidebook to Trewissick, written by the local vicar, in an old trunk. The boys are thrilled, but Jane feels suspicious and declines to join them. Withers and his sister Polly, who invite them to go fishing on their yacht. The family are visited at the Grey House by a very friendly Mr. The children decide to keep the discovery to themselves. They recognise a drawing of the local coastline that may be a kind of map, with almost illegible text, but Barney realises that the map refers to King Arthur and his knights.

In the attic of the big Grey House they are renting from Merriman's friend Captain Toms the children find an old manuscript. The Drew family meet him in the fictional fishing village of Trewissick on the southern coast of Cornwall. Over Sea, Under Stone features the Drew children, Simon, Jane and Barney, on holiday with their parents and Merriman Lyon, an old family friend, usually referred to by the children as their great-uncle. Thus it may ease readers into the fantasy genre.

In contrast to the rest of the series, it is more a mystery, with traditional fantasy elements mainly the subject of hints later in the narrative. Cooper wrote four sequels about ten years later, making it the first volume in a series usually called The Dark Is Rising Sequence (1965 to 1977). Over Sea, Under Stone is a contemporary fantasy novel written for children by the English author Susan Cooper, first published in London by Jonathan Cape in 1965.

The Grey King by Susan Cooper