Secret Water is the eighth book in Arthur Ransome's Swallows and Amazons series of children's books. It was published on 28 November 1939. This book is set in and around Hamford Water in Essex, close to the resort town of Walton-on-the-Naze. It starts only a few days after We Didn't Mean to Go to Sea ends. It brings the Swallows and the Amazons together and introduces a new group of characters, the Eels and the Mastodon. Ransome used to sail to Hamford Water, an area of tidal salt marshes and low-lying islands, in his yacht Nancy Blackett. He set the book here to offer his characters new opportunities to explore and make maps in a different landscape. Plot summary The Swallows intend to sail in the Goblin (as featured in We Didn't Mean to Go to Sea) to Hamford Water and camp with their father, but he is called away on naval business. To compensate, he maroons them with a small dinghy on an island. Before he leaves, Father gives them an outline map of the area they decide to call Secret Water, and suggests they survey and chart the area before he returns to pick them up. For the first time, their small sister Bridget accompanies them on this adventure. Titty and Bridget then find some mysterious footprints, which they think look as though they were made by a Mastodon; when nobody else seems to have any interest, they return to their camp, where they find a totem pole of an eel. They spot somebody escaping in a dinghy, and they track the person to his lair; it turns out that the footprints had been left by a local boy named Donald, whom they nickname the "Mastodon", wearing "splatchers" (mud-shoes), and he left the totem pole because he mistook them for the Eels, another family who camp in the area regularly. For a surprise, Father has arranged for the Amazons to come down from the Lake District and join them with another dinghy, named the Firefly. The Amazons then suggest that everybody becomes "blood brothers", which, after Bridget pricks herself from hunting berries, they do successfully. They take the Mastodon as their native guide, and they chart several islands. Later, the Eels arrive, and are initially hostile—to the point of kidnapping Bridget—but when they discover that the protagonists are now blood brothers of the Eels, they settle down for