The primary focus of the plot takes place during the final years of World War II, but it is framed by the story of present day 15-year-old Tamar's search for the truth.
In 1944 London, two special operations executives, Dart and Tamar, prepare to return to their native Holland as undercover agents for the English. They undergo intensive training, including simulated interrogations by Nazi officers, in order to help them be ready for any scenario. Just before their assignments, their orders are changed. Instead of actively working to liberate the Dutch, they will work to unify the already established but disorganized native resistance groups in Holland.
Dart's fake identity is not changed. He will become Dr. Ernst Lubbers. He will live undercover at a small psychiatric hospital, but his true mission will be to serve as the primary radio transmitter to England. He will transmit from three different locations in the town in order to keep the German radio detectors from pinpointing his position.
Tamar worries that he'll have to learn a whole new persona in a limited amount of time, but his commanding officer puts him at ease. His identity has been changed, but he will assume a role he's played before, that of Christiaan Boogart, an itinerant laborer. It is imperative that the bickering resistance forces come together, as each time an individual group makes a small strike against the Germans, the Nazis retaliate by killing Todeskandidaten, death candidates. These prisoners of war are held in camps and periodically dragged out in front of villagers to be shot as a warning against future terrorism. A few days after they receive their new assignments, Dart and Tamar parachute into Holland.
Tamar nearly dies of fright when a Nazi officer greets him as he is suspended in a tree from his parachute. The Nazi is actually Koop deVries, a leader of one of the renegade resistance armies. Koop brings Tamar and Dart to the Maartens' farm. It will be Tamar's hideout and one of the stations from which Dart will transmit to England. A young boy opens up the barn door where the SOE agents will hide their equipment. Tamar leads Dart to a hidden second floor. He explains that he transmitted from this same farm a year ago.
As Dart sets up the radio, Tamar returns to the ground floor of the barn. There he reunites with the boy. The two share a tense moment in which it's obvious they have had a relationship in the past. Tamar admits nothing has changed, he is still in love. He removes the boy's hat to reveal a beautiful young woman, Marijke. Later that night, Dart is ensconced at the Mendlo Mental Asylum a few miles away. After setting up another radio, he transmits his first message to England, notifying them of his and Tamar's safe arrival.
The following day, Tamar is introduced to Trixie. She will act as a courier between Tamar and Dart. Trixie's aunt is a nun who works at the asylum so she can visit several times during the week without raising suspicion. When Tamar leaves to sort out things in the barn, Trixie giggles with Marijke, teasing her about her lover's return.
Trixie instructs Dart on the best way to enter town so he can set up his third transmitting station at the Marionette House. The owners of the house, Bibi and Pieter, have toured all over Europe with their puppets. Bibi pretends to have an ulcer on her leg that requires Dart, as Dr. Lubbers, to visit every few days to change its dressing. It also allows Bibi to sit in her parlor at the window, serving as a lookout for Dart as he makes his transmissions. Dart receives an urgent message from England and decides to take it to Tamar so they can decode it together. At the Maartens' farm, he meets Marijke and is immediately drawn to her. Tamar doesn't reveal his intimate relationship with her.
The story shifts to 1995. Fifteen-year-old Tamar must deal with the death of her grandfather William Hyde from an apparent suicide. After her father disappeared five years earlier, William and his wife, Marijke, practically raised Tamar. Tamar and her mother knew William was depressed after having to put Marijke in a home because of her dementia. She often spoke in Dutch. When Tamar would hear her grandmother speak her name, she'd ask her grandfather to translate for her. He told Tamar that Marijke said she loved her, that she would always love her. When Marijke began hording food in her room and speaking of Nazis, William became more depressed. A month later, he killed himself.
Dart and Tamar continue living undercover in Holland. Tamar has to leave Marijke for a short time to aid an Allied plan and help British prisoners escape. On his frequent trips to the Maartens' farm, Dart begins to fall in love with Marijke. Because he is also taking large amounts of an amphetamine to keep awake for his job, his dreams about her begin to take on a reality of their own. By Christmas, he is obsessed with thoughts of her and believes she secretly loves him, too. Tamar and Dart have arranged for an air drop of food to help the starving people of Holland. Tamar returns to the Maartens' farm dressed as Sinterklass, the Dutch version of Santa Claus. Tamar, Dart, Marijke and her grandmother share a wonderful Christmas dinner of roasted chicken and even a traditional English pudding.
Dart nearly chokes on a coin baked inside the pudding. Tamar explains that it's a weird British tradition that will supposedly bring him luck. Later, Dart goes to the barn to receive a message from the British. He hurries back to the house, convinced that Marijke is waiting for him. Instead, through the kitchen window, he spies Marijke and Tamar kissing passionately. He perceives their love as a personal betrayal and soon enters a downward spiral of drug induced paranoia.
For months, 15-year-old Tamar kept the sealed cardboard box her grandfather left her untouched. When she finally opens it, she discovers a collection of random items — an unfinished crossword puzzle, four maps, an old passport, a black-and-white photograph and a roll of money. Tamar doesn't understand the weird contents and tries to ignore them while she studies for her school exams. The box plays on her mind, however, and she calls her older cousin Yohannes.
Yoyo, as he's known, is 19 and from Holland, although he is going to college in London. He is actually a close friend of the family and not really related to Tamar. Tamar asks him help figure out the mystery of her grandfather's box. Yoyo is able to translate some of the words in the passport. It belonged to a Christiaan Boogart, a farm laborer. Tamar believes that her grandfather may once have been Christiaan Boogart, that the unfinished crossword puzzle was his way of saying she must try and decipher the clues in the box so she can get some kind of treasure or knowledge. The maps are all of the area surrounding the Tamar River in England, and the money is the way she can pay for the trip. Tamar spends the next month convincing her mother to allow her to travel with Yoyo during their summer vacation and figure out what her grandfather wanted her to know.
Tamar's mother finally agrees to the journey after speaking privately to Yoyo about her daughter's young age and the penalty for taking advantage of a minor. As they travel, Tamar realizes that the cash her grandfather left her is also a clue — $1,945. It must refer to the year 1945 when he worked for the British army. Her grandfather has marked different towns along the Tamar River. She and Yoyo travel to each one but cannot fathom what mystery the towns hold. Tamar does, however, get the odd feeling that her grandfather made this trip himself for some reason, so she continues to follow the map.
Dart's paranoia takes a dark turn as he convinces himself that Tamar has somehow seduced Marijke into having an affair. He believes Tamar is a manipulative coward and begins to hate his fellow soldier. Meanwhile, against Tamar's strict warnings, Koop deVries plans a raid on a shipment of meat destined for the German army. Dart learns of the plan and immediately tells Tamar. Tamar knows if Koop is successful, the Germans will retaliate by killing as many of the Todeskandidaten as they can. They will probably round up innocent civilians as well to send to the death camps. Dart must radio England with the news, while Tamar swears he will stop Koop's plan. Marijke fears that if he's spotted, the Nazis will kill him. Tamar promises her and Dart that he will return by morning. If he doesn't, Dart must escape the area with Marijke. Before he leaves, Marijke tells him she is pregnant.
Koop deVries and several other men set a roadblock out to stop the shipment of meat. The vehicle they stop, however, is not the truck, but the personal car of the highest-ranking Nazi officer in the area. Koop and his men panic, firing their machine guns into the vehicle until their rounds are spent and they are certain the officer is killed. They then flee to hideouts in the woods. The officer is not dead. When he wakes up from surgery the following day, he asks how many bullet holes were in his car. When informed that there were 243, he insists that 243 prisoners be lined up and killed. As there aren't that many prisoners in the nearby camp, other camps are notified throughout Holland. The next morning, the prisoners from the local camp are taken to the scene of Koop's ambush and shot while prisoners in other towns are shot in their village squares. Koop and his men attempt to mollify their guilt by attending the executions. They hope to shoot the German guards and give some of the prisoners a chance to escape, but they are too late. Tamar finds them and angrily denounces their stupidity. Koop and Tamar argue bitterly. Tamar tells them to go back into hiding; he knows where to find them. Dart is nearly captured by the Germans who have traced his radio signal to somewhere near the Marionette House. Fortunately, he and Bibi are able to redirect the Nazis' attention so they don't search the attic upstairs and find his equipment. Dart convinces himself that Tamar's order that he not transmit from the Maartens' farm is the reason for this close call. Dart is sure Tamar wants him taken prisoner to keep him from Marijke. He begins to make plans to get rid of Tamar.
Dart gets his chance when Koop DeVries looks for medical aid at the asylum after being shot. Koop's fellow conspirators have been killed by German soldiers who found their hideout. Koop is sure that Tamar and Dart turned him in as retribution. Dart assures Koop that he had nothing to do with the ambush, but Tamar probably did.
Fifteen-year-old Tamar is questioning the purpose for following the marks on her grandfather's maps. They have led nowhere. Yoyo tries to convince her that it was her grandfather's way of telling her how beautiful she is, as the river has become more beautiful the farther they travel. Tamar knows they must return to London soon, but they follow the trail to the last stop on the map. Walking back to Yoyo's car one final time, Tamar is surprised to see a Land Rover parked nearby. The same car passed them on the road earlier, and it stopped as if the driver was watching them for some reason. A man exits the Land Rover. Tamar recognizes him as her father, Jan. Bewildered, she and Yoyo follow her father to his nearby home where Jan explains what happened that made him abandon his family. A few weeks before Tamar was born, her grandfather had asked him to consider the name Tamar for the baby. He alluded to the fact that it was in honor of his service in the war, as all the men he'd served with had been named after rivers in England.
Around the time Tamar started school, her father became obsessed with finding out more about his family's history, but neither his mother nor father would talk to him about it. Over the course of several years, his job gave him contacts within the British military, and still no one could give him information about his father's assignment. Eventually, while on a business trip to Holland, he put an advertisement in the paper for information regarding an officer in the resistance named Tamar. Jan was contacted several weeks later by Rosa, Trixie's daughter, who eventually arranged a meeting for him with the former resistance courier. Trixie was overcome with emotion when she saw a picture of Marijke and her husband. When she was able to speak again she told Jan that she had never been sure what had happened to her friend. She asked who the man was in the picture, and Jan explained that it was Tamar, his father.
The story shifts back to the past. Dart brings Koop DeVries to the Maartens' farm. He sends Koop to the barn to wait for Tamar while he runs to the house to tell Marijke to pack; they're escaping. DeVries kills Tamar, but when Dart returns to the barn to kill Koop, DeVries is waiting in ambush. Koop is angry that Dart thinks he's stupid enough to trust him. Koop turns his gun on Dart but is shot by Marijke. Once he's dead, Marijke discovers Tamar's body. She is overcome with grief.
Trixie recalls the day she found Tamar's and Koop's bodies in the barn. She could never fathom what had happened to Marijke as she knew her friend would never have left Tamar willingly. Trixie continued to stare at the picture Jan gave her of Marijke and her husband. She suddenly began to speak rapidly in Dutch to her daughter. Rosa seemed appalled at what her mother told her. Rosa took Jan out to the garden so they could talk. She warns him that her mother was upset and the events she's trying to remember happened years ago, so they may not be correct. She then told him that the man in the photograph is not Tamar, but Dart. Jan put the pieces together about Dart's betrayal and how he had murdered his father.
Once Jan returned home to England, his life fell apart. He had this terrible secret he couldn't share with anyone without destroying their lives as well. Jan became an alcoholic and eventually lost his job. He finally decided that to disappear would be better for everyone. He could start a new life without an imposter as his father, and his family could find a happier life without him. Years later, Dart tracked Jan down to try and explain what happened, but Jan wouldn't listen. Jan is convinced that Dart never loved any of them, that he was a manipulative man consumed with guilt for what he'd done. Tamar reminds him that it was her grandfather (Dart) who asked Jan to name her after his real father.
In an epilogue written some 10 years later, Tamar is living in Amsterdam with Yoyo. They are expecting their first child. If it's a girl, they will name her Marijke.