In war-torn Poland, the Balicki family lives under Nazi occupation after the German invasion. Someone informs the Nazis that Joseph Balicki, a schoolteacher, has turned Adolf Hitler's picture to the wall; for this infraction, he is arrested and sent to Zakyna, a brutal work camp in the mountains of Southern Poland. Anxious to escape, he becomes sick, and it is eighteen months before he is well enough to put this plan into action. He manages to hit a guard with a small stone shot from a catapult, knocking him out and giving Joseph time to take his uniform and wear it; in this way, he is able to leave with the other guards. He hides in a cable car and is discovered by a Polish peasant; the peasant and his wife hide Joseph for a couple of weeks, at great danger to themselves.
Joseph walks for a month until he reaches Warsaw, but finds his family gone and his home burned down. His old neighbor tells him that the Nazis took his wife away and his children are most likely dead. He is picking over the rubble of his home when he spots a letter opener his wife had given him in the shape of a silver sword. He turns to see a boy watching him; the irascible and wild boy wants Joseph to give him the sword. Joseph agrees to do so on the condition that the boy, whose name is Jan, tells his children (should he run into them) that Joseph is making for their grandparents' home in Switzerland, and that they should meet him there. Jan agrees, and also returns the next day to help Joseph jump a train without being spotted.
After Joseph was arrested, the Germans took his wife to work in the labor camps. Now their three children, Ruth, Edek and Bronia, who managed to escape the house after Margrit was taken, live in the cellar of a ruined house. Food is sparse, but Edek is a gifted smuggler and brings what they need. Ruth starts a school in the cellar; when she mentions this at the soup kitchen, she is given school supplies and a Bible.
In the summer they leave the city for the woods and Edek constructs a house with branches. Food is plentiful because the peasants are kind. Edek becomes one of the chief smugglers; he is calling at a house in a neighboring village when the secret police arrive and find cheese sewn into the lining of his coat. They take him away, and for two years there is no news of him.
In August of 1944, the sisters realize things are changing. The Russians were coming to liberate Warsaw, but the Poles end up taking the city back themselves. Running short of munitions, General Bor radios the Americans and British for help. By January 1945, Warsaw is in Russian hands and the Nazis have gone. Ruth and Bronia are shocked when they return to Warsaw and see it is decimated, but they find the cellar they lived in before, and set up home there. Ruth starts her school up again.
One day, Bronia and other children find a scrawny boy outside passed out from hunger. When he wakes, he tells them his name is Jan, but he is not very friendly. At first, he is too ill to leave; once he is well again, he decides to stay. With him is his pet cock, Jimpy.
Ruth visits the Russian control post and asks for food, clothes, paper, pencils, and help in finding Edek. The sentry, Ivan, is kind and brings them as many supplies as he can. Jan, who harbors a fervent hatred of soldiers, scuffles with him, and Jan's wooden box of treasures breaks to reveal the silver sword. Ruth recognizes it and begins to cry. Jan tells her of meeting her father, and Ruth decides they must leave Warsaw for Switzerland. First, though, they will stop by the camp where Edek was sent.
Ruth, Bronia, and Jan leave in the spring and head to Posen searching for Edek. They find that he has now been sent to a camp for children with tuberculosis; however, when they reach it they learn he ran away. They press on to Kolina for food; when Ruth is caught up in a scramble for food at the soup kitchen, she is saved by a hand grabbing her and sees it is Edek. He looks older and more haggard than Ruth remembered.
Reunited, the children travel by train with hundreds of other refugees going to Berlin. After nine days, they arrive and find the city in shambles. They are directed to a transit camp that is safe but overcrowded. They hear a chimpanzee has escaped from Berlin Zoo and bitten a policeman. Jan disappears into the city and finds the ape. Bistro, the chimp, is immediately respectful to him; Jan leads him down the street back to the zookeepers.
The family takes the Potsdam Road and jumps on a cart that takes them into the American zone. Despite pleasant summer weather, Edek is no better. However, he is determined to find out where Jan is stealing food from, so he follows him. His poor health and lack of understanding Jan’s plan makes him slow, and he manages to get both of them caught.
A Captain Greenwood is investigating what happened when Ruth, Bronia, and Jan appear in the courtroom. Ruth tells him Jan is the thief, and Captain Greenwood gives him seven days' detention.
The children continue their journey and hide in a barn for shelter but are discovered by the owner, Kurt Wolff. After an initial altercation, he invites them into his house where they stay as part of the family. Jan forms a special bond with their dog, Ludwig, who used to belong to their son, a soldier who was killed in action.
The children have to hide whenever the Burgomaster comes around; this official has the job of sending refugees back to Poland. They tell the Wolffs about the silver sword, and it is given pride of place on the mantelpiece.
The next day, Edek hears a jeep in trouble and goes to help the driver. His kindness unfortunately backfires: the driver is the Burgomaster, who pays the Wolffs a visit and tells them that the children have to return to Poland on the transport lorry leaving at noon the following day. His pleas for the children falling on deaf ears, Kurt Wolff devises a plan for their escape. He finds two canoes that belonged to his son and puts them together so that the children can use them to make their getaway.
In the early hours of the morning, Ruth and Bronia set out in one canoe, the boys in the other, with an additional stowaway passenger in the devoted Ludwig. They float downstream with the current, but the moon makes them visible from the banks of the river. A soldier clambers into the water to try to stop them and even tugs a paddle away, and there are shots fired from the bridge. They continue down river but have to get out and push when they run aground. They float over the water until they get to the mouth of the Danube.
Finally, the children walk into the town of Falkenburg, then get a lorry lift to Switzerland. Jan realizes in horror he has left the sword on the Wollfs mantelpiece, and wants to go back for it. They wake to find him gone, so Ruth sets her attention on getting her brother, sister, and herself further into Switzerland. Edek can walk no further and collapses; luckily, an American soldier drives by and picks them up. He turns out to have picked up Jan as well, after finding him asleep in the back of the truck.
Joe, the Polish-American soldier, drives them to a refugee camp and persuades the authorities to take the children in, but the camp superintendent refuses to allow them to cross the border into Switzerland without proof of identity or family vouching for them. Ruth writes to the Wolffs for the sword to be sent, thinking this might help prove their identity.
One day, Ruth is called into the superintendent’s office; he asks her to describe the sword in detail. She does, even mentioning the little piece on the hilt that is bent. He unrolls a parcel on his desk and shows her the sword, along with two letters: one from Herr Wolff and one from her father. Herr Wolff had pieced their family history together and sent it in the letter to the camp.
Joseph Balicki is living on Appenzell on the other side of the lake. He will collect the children by boat, and promises to telephone Ruth. However, the connection is bad and they cannot talk in much detail.
The Swiss boat set to take them over the water is not due for hours, and the children decide to take a walk. The air is heavy, but they do not notice. Ruth, Bronia, and Jan walk further to see if they can espy the ship, and the weak Edek stays behind. Suddenly, with one huge downpour of rain, the lake grows choppy and they cannot see where they were. They try to go back for Edek, but it is almost impossible in the storm. Ruth clings onto a little rowing boat, and she asks Jan for help. He has to choose between saving Edek or Ludwig; though it is a wrenching decision, he chooses Edek.
When Ruth opens her eyes, it is dark and she is lying in a bunk. She hears her father’s voice, and within seconds, she is in his arms. He shows her her siblings in neighboring bunks, but has left the biggest surprise for last: he has found their mother. Ruth feels a happiness she cannot describe. Her mother has clearly suffered greatly as a prisoner in Germany, but is filled with joy. Jan tells her he lost his treasure box, but he shows her the silver sword tied tightly on a string around his neck.
The family starts a new life in Appenzell, building a village for children orphaned by the war. Jan is adopted by the Balickis, although he is still wild and only Ruth can really handle him. Bronia is least affected by the war and flourishes, but Ruth becomes clingy and follows her mother everywhere. Eventually, though, she becomes confident again and goes to university in Zurich, qualifying as a teacher and marrying a Frenchman working in the children's village. They set up home in the house opposite her parents.
Margrit Balicki keeps her most treasured possession, the silver sword, in a velvet-lined drawer in her jewel box.