Set in Brazil in 1901, plantation owner Christopher Leiningen (Charlton Heston) makes arrangements to get married. He has spent his entire life building his estate and reclaiming land from the jungle. He is fiercely independent but he is also alone and isolated. Joanna Selby (Eleanor Parker) from New Orleans agrees to marry him but their first meeting does not go well. Leiningen is unhappy to discover that Joanna is a widow and hence has a past, so he tells her to return to America on the next available boat. However, local commissioner (William Conrad) informs Leiningen that swarming soldier ants, or Marabunta, are moving towards his plantation destroying everything in their path. Leiningen refuses to abandon his life’s work and is surprised when Joanna decides to stay with him. Can they convince their native workers to stay too and can they defend the estate from the Marabunta, described as “forty square miles of agonising death”.