It's election time at Mouseford Academy and the candidates from the Lizard and Gecko student clubs face some challenges if they want to get elected president. Certainly not helping matters is the arrival of a mysterious black ship off the shores of the island . . . and it's trying to pollute the beach! The girls must use all their investigative skills to root out the connection between the ship and the campaign. The fates of the election and their beautiful island home is at stake!
The school year at Mouseford Academy has begun, and a new student body president is to be elected. The student body is always run by two different students, one boy and one girl. The nominations are piling up, and the rivalries between nominees is getting hot.
One suggested nomination is Vanilla de Vissen, daughter of Vissia de Vissen. Vanilla, however, has a different idea and nominates one of her friends to be the female student body president. Not that she thinks her friend will do a better job. Only that Vanilla feels that she is easily manipulated and that any of her underhanded subterfuges can be handled more easily through a puppet.
The nominations are not handled traditionally as they are in other schools. First, the nominees accept to run. Then, they compete in three different contests to determine the winner of the title of student body president. During training for one of these events, Vanilla learns about the other contestants, and hatches a plan to give her friend a 'winning edge.'
Later that night, word is going around town of a mysterious ship that has been sailing around the island. One that never has any of its lights on. Most of the local fishers believe it to be nothing more than a tall tale of a ghost ship. That same night, Dina, another competitor for student body president, sprains her ankle in a very convenient accident, and is disqualified from the competitions. Nicky, who is friends with Dina, offers to take her place in the competition.
The next morning, Vanilla is pleased by the success of her plan, but is dismayed to hear that a more formidable competitor is now involved. Thus, she begins floating rumors in the hopes to get Nicky disqualified.
The competitions are soon underway. Nicky is nearly barred from competing due to the rumors, but is easily absolved of any wrongdoing. The first competition is to solve a difficult puzzle. Not Nicky's strong suit. With a bit of ingenuity, she is able to finish second.
The next competition is orienteering. Nicky knows now that she is at an edge, having been raised in the outback of Australia. After a long trek through the wilderness of Whale Island, Nicky nearly finishes the competition in record time, only to find that Vanilla's plant had won by a mere 58 seconds sooner, owing to having the path secretly marked for her.
Finally, the last competition. A marathon run. Also Nicky's strong suit. She begins strong and nearly has the win, until she notices something. A seal pup has washed ashore, and is covered in a sickening pink sludge. She tries to flag down help, and is answered by one of the other competitors and by one of the event supervisors.
Seeing the other competitors occupied, Vanilla's plant believes she has an easy win. What she did not know is that the event supervisor has reported the unusual find on the beach and the competition is suspended until further notice.
Dina's fiance takes the Thea Sisters out to sea in his boat to investigate the cause of the seal pup's condition. Miles offshore, they discover a gigantic slick of the pink sludge floating on the water.
Violet quickly comes up with a solution to clean the slick. Later, Paulina is overlooking a map of the island to track where the sludge likely had drifted from. Her plan is overheard by another of Vanilla's friends, who reports to Vanilla. The news worries Vanilla deeply. Not for any concern about pollution, but for her mother.
The Thea Sisters connect the dots over the mysterious 'ghost ship' and the pink sludge, both of which can be corroborated from the same destination. The ship is boarded by the authorities, and the crew implicates Vissia de Vissen of the wrongdoing. Once more, when she is confronted by the authorities, de Vissen is able to spin the truth and pay her way out of trouble.
One week later, the marathon race is back on. Though she tries with all her effort, Nicky is outraced by Tanya, one of the other competitors. Vanilla is at first enraged by the result, but then realizes that Tanya has a crush on Vic, Vanilla's twin brother. And an opportunity to control the student body president presents itself once again.