In the final 23 days of L's life, he takes on one final case involving a bioterrorist group that aims to wipe out much of humanity with a virus. The virus has an infection rate that is one hundred times the infection rate of the Ebola virus. During this case, he takes a young boy with a gift for calculations, the sole survivor of the virus's use in a village in Thailand, and an elementary school student named Maki Nikaido under his wing.