Over Sea, Under Stone
Susan Cooper
 Over Sea, Under Stone features the Drew children Simon, Jane, and Barney on holiday with their parents and their great uncle Merriman Lyon, in the fictional fishing village of Trewissick on the southern coast of Cornwall. In the attic of the big Grey House they are renting, owned by Merriman's friend Uncle Toms, the children find an old manuscript. They recognize a drawing of the local coastline that may be a kind of map, with almost illegible text, but Barney realises the map refers to King Arthur and his knights. The children decide to keep the discovery to themselves. The family are visited at the Grey House by a very friendly Mr. Withers and his sister Polly, who invite them to go fishing on their yacht. The boys are thrilled, but Jane feels suspicious and declines to join them. While Jane is alone in the Grey House, she finds a guidebook to Trewissick in an old trunk, written by the local vicar. 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. The man at the vicarage is not the writer of the guidebook, but he offers to help Jane. He asks some probing questions which arouse Jane's suspicions again, and she decides to return home. Soon the house is robbed with attention only to the bookshelves and wall hangings, and the children guess someone else knows of and seeks the manuscript. The children decide it is time to confide in Great-Uncle Merry. Up on the headland they show him the map and he tells them that it is a copy of an even older map which shows the way to a hidden treasure and that the children are now in great danger. He explains that some British artefact may have been stashed here long ago, and to confirm that they will have dangerous grown-up rivals in its pursuit. And so begins their quest for the Grail on behalf of the Light, which they have to achieve while being harried by Mr Withers and his sister, who are agents of the Dark, desperate to stop them at any cost. Mother usually paints outdoors, and father goes boating, or both travel out of town. Meanwhile the children investigate the meaning of the "map", encouraged, yet warned and sometimes "guarded" by Great Uncle Merry. They learn to read the diagram, and work out the clues on the map but they must work out of doors, where each child has a nasty encounter with the Dark, and their progress is easy to observe. While looking for the first clue Simon is chased by Mr. Hastings and Bill Hoover Jr.. After the second clue leads them to the headland at night, Simon, Jane, and Great Uncle Merry are ambushed and almost caught by Dark followers. Merriman is misdirected out of town, but the children anxiously follow their ancient guide "over sea and under stone" without him. Barney is kidnapped by Mr. Withers and his sister Polly, and must be rescued. The children eventually follow the clues to a cave off the headland and discover the grail. Unfortunately they lose an important metal case that was lodged inside the Grail, which contained a coded manuscript that is the key to deciphering the markings on the outside of the grail. The children present the grail to the British Museum and are given a check for it. The grail is an object of hot debate among the scholars there because of the unknown markings.