Tūpuna Rock is a tale of two teenage siblings raised in Canada by their Māori mother and Canadian father. While on vacation in Aotearoa New Zealand, their borrowed sloop is disabled in a storm with only the two teens aboard. Having lost their navigation gear, after six days adrift with no sense of direction, they beach their damaged boat on a desolate 'rock'. With no idea where they are and their boat damaged beyond repair, the teens recognize that they cannot save themselves unless they listen to the spirits of their Polynesian ancestors. Recalling knowledge shared by their Māori grandparents and basic science and mathematics, the protagonists reinvent enough traditional non-instrument navigation to determine where they are, design and build a boat and plot a course to sail one thousand kilometres back to Aotearoa after more than three months on their 'rock'.

Tūpuna Rock is written to appeal to a broad range of ages, including secondary-school students among whom engagement in science and mathematics is often declining, particularly among indigenous students. The reader becomes invested in the protagonists and their situation on a purely human level in the novel's first two chapters. In subsequent chapters the protagonists come to understand and value ancestral knowledge in the context of modern science and mathematics. In the process, the teens teach each other, and the reader.