A mail-order bride faces the perils of life in the Amazon jungle, including a horde of soldier ants.

In the jungles of South America, in 1901, Joanna Leiningen of New Orleans travels by river boat to meet her new husband Christopher for the first time. As they near the Leiningen cocoa plantation, Joanna, who was married by proxy, quizzes the local commissioner about Christopher, but he divulges little. After disembarking at the plantation, Joanna meets some of Christopher's native workers, including Incacha, his "number one man" and Zala, her personal servant, who shows her to her bedroom. That night, Joanna finally meets Christopher as he comes in from the jungle, sweaty and disheveled. Christopher is startled by his beautiful, refined wife, and although she assures him that she is ready to fulfill "all her marital obligations," he is formal and abrupt with her. When Joanna reveals that she was moved by some of the lonely letters he sent to his brother, a friend who was put in charge of finding Christopher a wife, Christopher bristles at the suggestion of weakness and departs. The following evening, Christopher orders Joanna to play the new grand piano he bought for her and then asks if she speaks any foreign languages. After uttering some French, Joanna accuses Christopher of treating her like a commodity, and he complains that she is too "perfect" and must be hiding something. When Joanna admits that she is a widow and that her previous husband was a drunk, Christopher, who has lived in the jungle since he was nineteen and has no experience with women, rejects her as "used." Later, Joanna witnesses a native execution and criticizes Christopher for doing nothing to stop it. In response, Christopher gives Joanna a tour of the plantation, pointing out the prevailing cruelity of jungle life, including a shrunken head coveted by Kutina, his most loyal worker. Repulsed, Joanna retreats to the house and barely speaks to Christopher, annoying him with her silence. When she retires to her bedroom and begins undressing, he sees her silhouette through the window and becomes aroused. After drowning his confusion in drink, Christopher breaks down Joanna's bedroom door and grabs her, then sensing her revulsion, pushes her away. Christopher confesses that he cannot accept another man's "leavings," and Joanna agrees to return to New Orleans on the next boat, which is due in a few weeks. Later, the commissioner returns to the plantation with Gruber, another American planter, who has accused Christopher of stealing two of his contracted workers. To keep the sadistic Gruber from taking his men back, Christopher accuses them of murder, and the commissioner goes along with the ruse until Gruber finally leaves, angry but empty-handed. That night, the commissioner dines with the Leiningens and is saddened to learn about Joanna's departure. However, the commissioner's concerns about Christopher's emotional state are quickly overshadowed by his current mission¿to investigate why birds and monkeys have been fleeing the jungle around the Rio Negro. When the commissioner confesses his suspicion that the source of the problem is "Marabunta," Christopher insists on accompanying him to the Rio Negro and then tells Joanna that she is leaving with them in the morning and will be catching the mail boat upriver. Although Christopher apologizes to Joanna and admits he is confused and uncertain, he maintains that she will be better off in New Orleans, single again. The next morning, Joanna, Christopher and the commissioner head for the Rio Negro with a group of natives, and while camped that night, become aware of an eery silence. Sensing danger, Christopher insists they decamp immediately, and the following day, they come across an abandoned village. After Gruber's body is discovered with its face eaten away, Christopher leads the others to a hilltop overlooking a valley. Down below, the ground appears black, and Christopher informs Joanna that the valley is swarming with Marabunta, billions of soldier ants, who are eating their way across the jungle. Christopher calculates that the ants will reach his plantation in one week and declares he is fighting the invasion. At Joanna's insistence, Christopher takes her back to the plantation, then convinces his terrified workers to stay by pointing out the bravery of his "woman." With little time to spare, Christopher directs his men to create a moat around the walled-in plantation house, hoping the ants will not be able to cross the water. On the eve of the ants's anticipated arrival, Christopher and Joanna finally admit their feelings for each other and kiss. The ants arrive the next day, devouring everything in sight, and begin floating across the moat on fallen leaves. Christopher orders everyone to retreat to the plantation house and rings the walls with fire, using furniture as fuel. Although the fire diverts the ants, Christopher runs out of furniture before they have completely passed. The next day, Christopher covers himself with oil--ant repellent--and dashes with some explosives to a large dam upriver. After setting the explosives, Christopher scrambles away, then is swept up in the ensuing flood of water. The overflowing river drowns the remaining ants, and Joanna is greatly relieved when her husband stumbles out of the water and into her arms.