The Famous Five - Book 6: Five on Kirrin Island

Five On Kirrin Island Again is the sixth novel in the "Famous Five" series by Enid Blyton. It was first published in October, 1947.

The Famous Five is the name of a series of children's novels written by British author Enid Blyton.
The novels feature the adventures of a group of young children — Julian, Dick, Anne and Georgina(George) — and their dog Timmy.
Three of the children, Julian, Dick and Anne, are brothers and sister. During their holidays, they are regularly sent to the seaside town of Kirrin to stay with their Aunt Fanny and Uncle Quentin, whose daughter, Georgina, is a tomboy who insists on being called George. George owns a large mongrel  dog, Timmy, who is very much part of the group and a character in his own right. Timmy accompanies the four children on every adventure.