Mae and Clintion are fighting about whether a new vaccine is safe. But when protests against the vaccine threaten to turn violent, Selectra Volt insists that the two middle schoolers go on a mission together to find the truth. Mae and Clinton travel through time from ancient India to Europe, Australia, and North America. They witness the fight against smallpox, rabies, polio, and other viral illnesses as they visit Louis Pasteur, Jonas Salk, Macfarlane Burnet, Maurice Hilleman, and Andrew Wakefield.