The Thea Sisters uncover a conspiracy to destroy the environment during the heated competitions for student-club presidencies. Mouseford Academy's two student clubs, Lizard Club for girls and Gecko Club for boys, are selecting new presidents. Each club's candidates compete in three competitions--"brainpower, crafts, and sports"--and the mouse with the most points at the end wins. The Gecko candidates are athletic Craig, nerdy Shen and mysterious Vic de Vissen. On the girls' side, when Vanilla, Vic's sister (and fellow child of the antagonist from The Secret of Whale Island, 2013), learns the Thea Sisters' friend Dina is competing for the Lizard presidency, she decides to cheat so her friend Alicia can win the post instead and use it to trouble the Thea Sisters. The third Lizard candidate is cheerful Tanya. The stakes of the contest are vague; tension relies on the readers' willingness to believe the cheaters might win. During the last event, seal pups covered in a mysterious, scented, pink substance appear on the island--evidence of chemical contamination. The Thea Sisters spearhead an investigation to catch the culprits dumping pollution into the ocean and find a familiar source. While there are too many characters for all to have distinguishing personalities, the varied character designs help readers keep them straight. The plot is uneven, but mild surprises and bright colors will appeal to reluctant female readers. (Graphic fiction. 7-10)