The story begins in the Murry household, but soon leaps back in time to ancient Wales where Charles Wallace must begin piecing together Branzillo's ancestry. There Charles Wallace observes the struggle between Madoc and his brother, Gwydyr. Eventually Gwydyr leaves for South America, to an area called Vespugia, a part of Patagonia where Branzillo now lives. Guadior takes Charles Wallace there, in the year 1865, to continue his search, which finally leads the unicorn and Charles Wallace to the time of Mrs. O'Keefe's youth.