Role in the film
Traveling from Bern, Switzerland to the new colony of New Guinea to avoid Napoleon Bonaparte's European conquest, Mother and her family find themselves caught in a raging storm when being chased by pirates and trapped in their room of the Titus, the ship they are sailing on. Mother and her youngest son, Francis, stay behind while her husband, Father, and two older sons, Fritz and Ernst, try to call for help but no one seems to be on board to answer their call until the ship gets caught on the rocks.
In the morning, Mother and Francis managed to get out after Father, Fritz, and Ernst help break free from their room. They find themselves shipwrecked next to a deserted island, the ship's captain and crew gone, and the farm animal livestock trapped inside along with Captain Wilhelm's dogs, Duke and Turk.
Mother and her family begin to build a raft out of the ship's wood and anything else they can find. Then they begin collecting all their belongings including guns and muskets from Captain Wilhelm's cabin and anything else they might need to survive.
Once everyone is on board, they begin to set sail while Francis complains to Father about leaving Duke and Turk behind as Father states they are "too heavy that might sink them." Against Father's wishes, Francis signals Duke and Turk to follow them by swimming despite the strong current. As Father, Fritz, and Ernst row while getting closer to shore, the current gets stronger by the minute, making it almost impossible for Duke and Turk to overcome it despite being good swimmers. Mother pleads Father to help them but he is not likely to take any risks. At the very last minute, when hearing them barking helplessly, he has a change of mind and heart and brings them on board the raft without any further incident, thus, proving his theory about sinking them wrong.
Once on shore, Mother calls Francis to rejoin them when she catches him running with Duke and Turk to a Galapagos tortoise. When Father suggests they make camp for the night, Mother suggests they first pray, which they voluntarily do. While Mother provides them with whatever food they have left and Francis feeds Duke and Turk, Father, Fritz, and Ernst try to pitch up a tent on the beach but to no avail while a tiger inconspicuously watches them. After finishing the tent, Father suggests to Fritz and Ernst to return to the ship tomorrow to begin loading all the animals. Then Mother screams at the sight of a monitor lizard, so Father comes to her aid and Fritz tries to shoot it but he can't since the gunpowder is wet.
At night, Mother wakes up to convince Father to sleep as well since he's staying on guard. They start discussing all the problems they've suffered and tried to avoid until it begins to rain, thus, forcing them to stay inside the tent.
The next morning, while Father, Fritz, and Ernst are out bringing the animals from the ship, Mother notices Francis is missing, so, she sends Duke and Turk to find him. They come just time to save him and a baby elephant, which he caught to be his new pet and later named Rocky, from the tiger. After Duke and Turk finish it off, Mother thanks them and scolds Francis for disobeying her but eventually comes to her senses and allows him to keep Rocky.
Later, Mother cleans some of the silverware and other belongings while Father and their sons, with Rocky's help, are building a treehouse somewhere within the island to keep them safe from the pirates that chased them into the storm and whom Father, Fritz, and Ernst tried to avoid during the day while bringing the animals from the ship, and some other predators living on the island. When Mother feels uncomfortable with all this, Father reminds her of the situation they are now in. Then, she is brought up by him to the treehouse to show her where they'll be sleeping soon but she still fears about falling off the edge (same for Francis' sake too). So Father brings her down while Francis catches and adopts a new pet monkey when nearly falling if not for the rope Mother tied around his waist for safety and Ernst holding him. Upset, worried, and scared, Mother instructs Father, Fritz, and Ernst to keep him on the ground while working on the treehouse and vows not to return until it is completed; something that Father reluctantly agrees on.
Days (or weeks) later, Father and the boys bring Mother back blindfolded to their new home. After removing the blindfold and allowing her to joyfully admire it, Father proceeds with an "old Swiss custom": carrying the bride across the threshold. She is shown around her by him: the latest running water innovations Fritz and Ernst invented and built, the kitchen, the cooler, and all the rooms. When she notices a rope in the room, she assumes it's to "ring for the butler" until Father shows her that it is actually used to open the ceiling so as to allow her to look at the stars at night as she once dreamed she would when they went to Interlaken one summer. However, she doesn't like the curtains they brought from Captain Wilhelm's cabin. Nevertheless, she is overwhelmed with joy that she feels she doesn't deserve it until Father comforts her and assures her that he knows "a woman who can fix anything" including the curtains.
A few days later, Mother is heard singing "My Heart Was An Island" as she fixes the curtains in her own design in her room while Father and the boys are out doing their duties. Then when she hears Francis shouting, she comes out of her room to find him and the rest of her family catching and riding an ostrich they later name Clementine, which Francis tried to catch first.
Later, Mother sits and watches Father and the boys spending the rest of the day having some fun swinging on vines in a nearby water area. After failing to swing like a monkey while Fritz succeeded and falling into the water, Mother and Father have a small conversation. With all this fun, he feels this is the kind of life they were probably meant to live in but she seems rather concerned about the future especially that of the boys when it comes to the idea of marriage and family. To offer a solution to all that, Father suggests they allow Fritz and Ernst to sail around the coast with the sailboat they've been working on so as to see what they can find and Mother reluctantly agrees since they are choiceless. So Mother, Father, Francis, and Rocky help prepare the sailboat for sailing and wish them luck. Mother also relies on Ernst's knowledge and way of thinking.
A couple of more days have passed and it's Christmas. Mother plays the organ they brought from the ship as Father sings "O Christmas Tree" and Francis enjoys his Christmas gift. Then Father offers Mother hers and comforts her when she starts worrying about their sons as Francis gets ready for bed. When she is on the verge of tears, she and Father hear some singing from a distance and decide to check it out. Out there, they notice Fritz and Ernst having returned home safe and sound and with a girl named Roberta, whom they saved from the pirates, riding on a new zebra named Duchess, which they rescued from predators.
Mother dresses Roberta up in a pink dress while Father and the boys discuss a plan on how to defeat the pirates since they are aware of Fritz and Ernst's actions. Then Mother comes down with Roberta and starts to play the organ as Father joins in dancing with her. Fritz and Ernst, both in love with her, try to get a chance to do so as well. Seeing as to how they are fighting over who should do so, Mother continues to play and Father decides to continue on doing so while Fritz dances with Francis, leaving Ernst completely depressed, partnerless, and jealous too.
The next morning, Mother, Francis, and Roberta watch Father and the boys blowing up the ship still stuck on the rocks with gunpowder so as to confuse the pirates about their location. Then, Mother, Francis, and Roberta begin to build some traps, snares, entanglements, and other sorts of weapons (like coconut bombs).
At night, after Francis, whom along with his family are preparing for the new holiday arranged by Father for tomorrow, has captured the tiger in one of the pit traps, an idea which he has had in mind for the pirates using a piece of meat as bait, Mother and Roberta stays in the treehouse while Father, the boys, Duke, and Turk come to see to it. Then Mother is happy to hear from Francis about getting his tiger.
The next morning, while the pirates led by their leader, Kuala, return to the island and begin looking for Roberta, Mother and her family prepare for the race of their new holiday. As Roberta and the boys race on their animals, Mother and Father watch them as they begin to hilariously foul-up due to the animals' behaviors. When Roberta returns after Duchess has had her unintentionally riding toward the beach, she warns Mother and her family about the pirates having finally arrived on the island. Everyone gets ready for their battle positions including the hill as their last battle position.
After the pirates are defeated by the false bridge, the crossbows, the pits including the one with the tiger, the traps, the snares, entanglements, gunpowder fuses including the ones on the boulders, Mother and her family throw coconut bombs at them. When they continue climbing up the hill, Father manages to get them running scared and possibly killed by rolling logs. When it seems that they get the upper hand, Kuala begins to talk to the Robinsons about a trade between the "boy" (Roberta) and their lives as a diversion while his pirates sneak up on them on the cliff behind them. Nevertheless, Mother and her family are not gullible enough to fall for Kuala's tricks. Then they managed to fight off the pirates with their guns and muskets on the cliff when they hear them coming; thanks to Francis' "pirate alarm", while Kuala and some of his pirates sneak upon them.
During the battle, Mother shoots some pirates trying to attack her and just when it seems that all hope is lost for them, cannons are heard firing. At first, they think it's the pirates firing on them until they notice that it's actually a British ship commandeered by Roberta's grandfather, Captain Moreland, another one of the pirates' former prisoners held for ransom, firing on them and their ship, thus, leading to Kuala and his pirates' deaths; much to Mother and her family's joy and victory.
After Captain Moreland has had a meal, offers to take Ernst to a university in England, and promises to take the family to New Guinea, Mother finally decides to remain on the island as their new home with her family and the animals; much to everyone's astonishment and joy especially Father's, and Captain Moreland notes that the former will likely be recommended as governor of the new colony.
Mother is last seen waving good-bye with her family including Roberta, who has decided to remain with them as well to marry Fritz, and wishing luck to Ernst as he travels to England for his education.
- In the original novel, Mother Robinson's real name is actually Elizabeth. However, in the film, it is unknown if her name was in fact Elizabeth too, since her name was never mentioned in the movie.