The general setting of Ian Serraillier's novel The Silver Sword is Warsaw, Poland, during WW II and after. Ruth, Edek, and Bronia Balicki are forced to survive on their own after their father was taken to a prison camp and their mother was taken to a labor camp in Germany.
Edek is separated for some time from his sisters; the girls eventually make their way back home and learn that their father is waiting for them in Switzerland. They leave for Switzerland, along with a neighbor boy named Jan, on a rather harrowing journey. Jan has the silver sword, a token of recognition from the children's father.
The children are eventually reunited and take refuge in a barn in Bavaria. This farm belongs to Kurt Wolff and his wife; when Wolff discovers them sleeping in a haystack in his barn, his first reaction is to turn them in to the local authority, the burgomaster who is supposed to send all Polish refugees back to Poland immediately. Wolff's wife convinces him to change his mind, and the children offer to work as payment for the night spent in his barn.
Because the burgomaster is doing his job diligently, the children would be in too much danger if they tried to leave, so they end up staying on the farm far longer than perhaps either they or the Wolffs intended. The children each do chores but are quite careful to stay out of sight whenever they sense any trouble or danger.
Eventually the children are caught. While the burgomaster is sympathetic when Wolff shares the children's plight, he insists on doing his job and says he will return to the farm the next morning to collect the children so he can send them back home.
Wolff ponders and finally decides that the children's best chance of escape before the authorities return is by water. He has two old canoes, and the children continue their journey in them. Edek and Ruth have each had some experience with canoeing, so they each take charge of one canoe. Young Bronia is Ruth's partner and Jan is Edek's partner. The Wolffs give them some supplies.
A short time into the journey, Jan realizes that there is something alive in one of the baskets the Wolffs gave them and discovers that the farmer's dog, Ludwig, has stowed away on the canoe. The children love having the company.
Of course it is night when they leave, and for a time all is well. The moon is hidden behind the clouds, giving them some cover as they paddle down the river past the village; unfortunately, the clouds pass and the moonlight reveals several trucks waiting in a field in town. Ruth understands that these are the trucks designated for refugees such as the four of them, and she is worried. At just about the same time, the two canoes pass under a bridge and are forced to navigate a strong current.
The boys' canoe gets by the danger, but the girls' canoe gets stuck at the base of the bridge. A soldier seems to come to their rescue but then tries to grab Ruth's paddle in order to haul the canoe (and the girls) to shore. Ruth and Bronia are able to escape when Ruth lets the paddle go, dumping the soldier back into the water. The girls are also shot at, though they are not hit.
The girls escape but are unable to steer without a paddle. The girls fall asleep until their canoe crunches over a rock. They panic but make it to shore where they begin walking downstream. They are hoping to meet the boys, and before long the girls do find them. Their journey continues on land.
It [is] true that, while they had the sword, fortune [was] kind to them.