In a fifth-grade classroom, Leo the tuatara and Squirtle the turtle face turmoil when their teacher Mrs. Salinas goes on maternity leave. Leo, nearing the end of his life, fears unfulfilled dreams, while Squirtle's jealousy leads to betrayal. Leo's secret ability to talk helps students with their problems until Squirtle exposes him, leading to Leo's abandonment. The students, with Ms. Malkin's reluctant help, embark on a journey to find Leo. Leo discovers he can live longer, renews hope, and is rescued by the students from alligators. As the school year ends, Leo advises unity, and Ms. Malkin gains redemption, becoming a teacher for kindergarteners with Leo and Squirtle as class pets.