Sabrina and her friend Gwen meet up in Australia to have fun exploring the Great Barrier Reef and meet a renowned oceanographer. However, before the girls meet the scientist, they discover Barnaby, a mermaid washed up on a beach with a rash on his fins. It is through helping Barnaby recover from his rash that Sabrina is able to meet Dr. Martin. Unfortunately the story that Sabrina tells the doctor arouses his suspicions about who Barnaby really is, and it almost gets in the way of the witches researching why Barnaby and the other mermaids in his community are getting sick. Meanwhile, Salem arrives at the same hotel Sabrina and Gwen are at for a vacation and soon falls in love with another talking cat.