In 1820, an island appeared from the sea. In Dublin Bay, right under the noses of Dubliners. Within years of the appearance of the island a nearby island called Clontarff Island disappeared.

There were several other islands, including one known as Sand Island and another called Green Island, but they too had disappeared. Tragically, a fisherman, a woman out walking and a number of others then also disappeared. This work is a history of Dublin's Bull Island, which lies just off Clontarf and has existed for less than 200 years. The book is a weave of social, ecological and personal history. The social component covers items such as notable shipwrecks, plundering, some prehistory (the Battle of Clontarf), Captain Bligh, James Joyce's 'bird girl', the island's many tragic suicides and one or two murders. The narrative also contains details about Clontarf and its environs, including references to the mainland adjacent to the island.

As Bull Island is an internationally famous bird sanctuary and nature reserve, the text covers the emergences of the island's bird life, its rich botany, the various historic threats to the island's ecology and the efforts of environmental activists and conservationists. On a personal note, the author describes an accident on the island in which a broken ankle led to a life-threatening blood clot. The book concludes by suggesting that Bull Island's ecological problems are a useful symbol for what is happening in our world. There is much we can learn from this island imagined by the sea.