In this fourth explorers adventure we meet Ursula, a part mermaid girl who is determined to help Stella defeat the Collector! Alex Bell deftly takes her readers to another enchanting corner of the Explorers Kingdom. Orphaned, but determined to make her way in the world, Ursula wants to follow in Stella Starflake Pearl's footsteps and become an explorer, even though she is 'only' a girl! But she has countless barriers in her way, not least the fact that she is part mermaid - and therefore the sworn enemy of all Ocean Explorers . . . When the mysterious and now much feared Collector threatens the very existence of the Club, however, Ursula does not hesitate to defend it, even though it puts her own future in jeopardy. At last it seems she will meet Stella and go on an expedition of her own - through treacherous waters -full of gremlins and far worse - aboard the Blowfish submarine, helped by the suspicious twins Genie and Jai Bartholomew Singh. Thrilling, heart-pounding adventure with exquisite detail throughout. Alex Bell's world-building is second to none. Children will adore this.