The wealthy orphan, Ada Payne, determines against the wishes of her guardian to go to Africa and join her lover, Jack Wilson, whom she supposes to be with Stanley's party. Meanwhile Jack and his chum, Tom Dixon, are returning to America with Nina Mannering, whom they have rescued from the Hidden City. They arrive in New York to find Ada gone and resolve to return to Africa and find her. Tom marries Nina and they start. Ada reaches the Hidden City. The guard left behind by Stanley can give her no information. It is an even chance whether he has joined Stanley or has returned to America or is dead. Ada, half distracted, resolves to push forward and join Stanley's party. Jack, Tom and Nina land on the coast and push forward to the Hidden City with various adventures with animals and natives. Stanley, seized with fever, is delayed weeks in an interior town. Jack, Tom and Nina reach the Hidden City and find that Ada has been there and has gone forward. Ada falls in with an eccentric old man with an elephant, known as the Jungle Rat. He becomes the companion of her wanderings. Stanley recovers and moves on up the Congo River by boat. Jack is seized with fever and lies at death's door. Ada is captured by natives. The Jungle Rat is left for dead. Stanley is attacked by natives, but beats them off and fires their town, escaping in the confusion.