Johnson, Gillian

When an attempt to steal Shirley, a rare sea-unicorn, results in the sinking of their houseboat, ten-year-old Thora, her mermaid mother, and Mr. Walters stay at the estate of old friends and find a solution to the friends' financial troubles, but the would-be thief is still on their trail.

Fabio the dog longs for the companionship of a feisty brother, so when the family brings home an older, sleepier sister, he is not very happy.

Ten-year-old Thora, daughter of a mermaid mother and a human father, has many adventures at sea until she must return to the English seaside town of Grimli and save her mother who has been captured by the greedy real estate developer, Frooty de Mare.