They were stranded and there was nothing around as far as they could see. This book is about their discoveries and their adventures on the island. Agatha kept journals, with the hope of someday they would be rescued. This is from her journals.
They called the island Rosland Island. They learned later it was once a mountain range connected to a mainland, and as time passed the mountain range sank into the ocean. Only Rosland Island was left, where once a land mass had existed. The island has two mountains on it, one at each end. There are many stories to tell about Agatha and Frank's adventures, and about who lived on the land mass, besides the Merbeings.
This is important to know, because of everything they discovered!