Ruth drives to Honolulu to meet a Japanese crewman at the pier during a Boat Day celebration. The man is actually a disguised naval intelligence officer. As the two pose as tourists, Ruth guides him around Oahu’s military installations; they observe Pearl Harbor, Ford Island, and the coastlines, then drive around the island while the officer studies the terrain and landmarks. The tour concludes at the Kuehn home, where the officer gathers more intelligence from Otto and Friedel. Ruth then drives him back to his ship.

This becomes Ruth’s routine, and the family explains their various Japanese visitors by claiming that they are returning hospitality for soirees that they enjoyed in Japan. As narrator, Christine Kuehn notes that the spy historian Kurt Singer calls Ruth the smartest spy in the family, for Ruth’s romantic relationships with American naval officers have provided the family with effective cover for their intelligence-gathering.

When a local paper reports Ruth catching the bouquet at her friend Herta Zarnikow’s wedding to Marquis Stevens, the FBI learns that Herta is a recent German arrival who does not speak English. Agents begin investigating Herta’s pro-Hitler husband.

As narrator, Christine Kuehn reflects on her grandparents’ decision to use their daughter for espionage and speculates that Ruth may have performed these duties as penance for being half-Jewish.

The narrative relates that the Kuehns first drew attention from US intelligence immediately upon their arrival in Hawaii. In February 1939, FBI Director J. Edgar Hoover orders a deeper investigation, but the lack of a permanent Hawaii office hampers the FBI’s surveillance efforts, as agents must make a series of limited trips from the mainland.

On March 15, Germany invades Czechoslovakia. Leopold writes to Otto, expressing pride in Hitler’s conquests and detailing his own political ambitions. A 1940 photo shows Leopold surveying the Spandau concentration camp’s subcamp; decades later, when Christine discovers this image, she is deeply disturbed to realize that Leopold may be directing his pitiless gaze toward Jewish prisoners off-camera. 

Meanwhile, Nazi influence spreads to the United States, where 22,000 members of the German American Bund hold a pro-Nazi rally in New York City.

In May 1939, Otto’s furniture company goes bankrupt. After he and a female passenger have a car accident, Friedel accuses him of having an affair and opens a separate bank account. In August 1939, the FBI opens a full-time Honolulu office under Special Agent Robert L. Shivers.

Shivers, a soft-spoken Southern white man, struggles to earn trust in Hawaii’s multicultural environment, so he hires Shizue Kobatake, a local Japanese American student, as his guide, nicknaming her Sue and introducing her as his and his wife’s adopted daughter. He builds contacts and learns that many Japanese Americans are loyal to the US, contrary to FBI headquarters’ belief that a plethora of Japanese Americans hostile to the USA must lurk in Hawaii. FBI Director J. Edgar Hoover sends a list of 125 suspects for Shivers to investigate, including the Kuehns.

Leopold sends the family a letter just before the invasion of Poland, blaming England and Jews for the impending conflict. Four days later, Germany invades Poland, beginning World War II.

After war breaks out, Hawaii’s defenses are fortified. The War Department declares the island impregnable, though military authorities remain more concerned about internal sabotage.

Between 1938 and 1940, Japanese payments to the Kuehns stop, causing financial hardship. In January 1940, Friedel purchases high-powered binoculars, which the FBI notes as suspicious. Desperate for money, she travels to Japan to get the payments restarted. Upon her departure, FBI agents search her at the port but find nothing.

Friedel arrives unannounced at Dr. Homberg’s home and finds him with another woman. After an emotional breakdown, she demands $40,000. Homberg gives her $6,000 in cash immediately, promising to send the balance later. Friedel returns in April with the money hidden under her clothes, and although FBI agents find it, they have no cause to detain her. She forces Ruth to break off her engagement to Homberg and creates a flimsy cover story about a property sale to explain the money.

In summer 1940, Shivers learns that Otto is frequently visiting the Japanese consulate, whose staff are known intelligence officers. The Kuehns deliver sensitive naval intelligence directly to Japanese officers there, which reaches Admiral Isoroku Yamamoto, the chief planner of the Pearl Harbor attack.

Otto receives a letter from Homberg about payment difficulties and suggests contacting an acquaintance of his named Baron Kyogoku “to help assist in getting the money from Tokyo to Honolulu” (105). Otto sends Homberg a dictionary for coded messages. In 1940, Navy intelligence classifies Otto as a class A Nazi suspect; Friedel is classified as such in May 1941.

On September 15, 1940, a Japanese steward named Mr. Kai arrives in Honolulu and calls Otto. They meet near the harbor, and Kai delivers $10,000 in cash and a note that instructs Otto to stop contacting Homberg. The new contact is Baron Kyogoku, whom Shivers concludes must be a code name for an untraceable handler.

Frustrated by the lack of evidence, Shivers taps the consulate’s phones and intercepts the Kuehns’ mail. Surveillance confirms that Otto’s Japanese language studies are a sham, and other informants report the Kuehns expressing pro-Nazi views at German clubs.

Meanwhile, Ruth and Friedel open the Kailua Beauty Shop to gather intelligence from naval officers’ wives. In the fall of 1940, Otto builds a dormer window on their house, which Shivers suspects is for signaling submarines.

Takeo Yoshikawa, now a decorated Japanese intelligence officer, is sent to Honolulu in late 1940 under diplomatic cover. Around the same time, Ruth begins a romance with Jacob Carson Moore, a 48-year-old widower with two children. Within six months, they marry and move near Otto and Friedel. (Ruth tells Moore nothing of her family’s activities.)

On April 10, 1941, Shivers orders that in the event of a war, Otto should be detained. As President Roosevelt freezes Axis assets, the Japanese consulate grows nervous about Otto’s frequent visits and arrange to communicate with him by a postcard signal system instead.

At the same time, 15-year-old Eberhard’s vocalizes his hatred of Nazis, causing his mother to restrict his associations. In a flash-forward to 1999, the author Christine recalls a trip during which she planned to discuss Eberhard’s past with him, but at the time, he experienced a grave memory lapse, and two months later, he was diagnosed with dementia.

By this point, Shivers is certain that the Kuehns are spies for the Japanese. The author relates that Dusko Popov, a “German spy turned double agent for the British Secret Intelligence Service, MI6” (119) then warns the FBI about Nazi interest in Pearl Harbor. Popov is also the historical figure who inspired British intelligence officer Ian Fleming to develop the character of James Bond. In August 1941, the Germans send Popov to the US to establish a spy network, after which he is to proceed to Hawaii to replace Otto, who is now considered a security risk.

However, British intelligence arranges for Popov to meet with FBI agents and show them his microdot orders, which contain detailed questions about Pearl Harbor’s defenses, clearly indicating a planned attack. Although J. Edgar Hoover personally meets Popov, he dismisses the double agent’s warning and does nothing with the crucial intelligence. Popov’s Hawaii mission is aborted, leaving Otto in place.

In October 1941, Nazis begin systematically deporting Jews from Germany. In Hawaii, the Kuehns face financial trouble yet again, and Ruth’s marriage proves unhappy. A paranoid Friedel suspects that Moore is an FBI agent, so Otto writes Moore’s former maid, seeking information about him. She does not reply and reports the letter to the FBI.

After Japan invades French Indochina in July, Roosevelt imposes a total embargo, crippling Japan’s economy. Negotiations fail by October, making war inevitable.

On October 25, 1941, Japanese diplomat Otojiro Okuda and Takeo Yoshikawa drive to the Kuehn house. Okuda hangs back while Yoshikawa encounters Eberhard and asks for Otto. He then gives Otto a package containing $14,000 and a note requesting a radio test. Otto writes a response saying that he cannot comply, then burns the note and alerts Friedel. This contact signals the activation of the Japanese mission to attack Pearl Harbor.

One week before the attack, Robert Shivers feels that a Japanese raid is imminent and shares his fears with Honolulu Police Captain John Burns. Military officials and newspapers remain confident that an attack is unlikely. On December 1, Shivers adds Friedel and Ruth to the enemy alien detention list.

Intercepted Japanese communications reveal escalating preparations. On November 1, disguised naval officer Lieutenant Commander Suguru Suzuki delivers 97 questions about Pearl Harbor to Consul General Nagao Kita. Takeo Yoshikawa provides answers, detailing Pearl Harbor’s patrol schedules, submarine nets, and ship readiness. On November 30, a Japanese message to Berlin reveals that negotiations have ruptured and that war may break out soon. On December 2, Tokyo signals the fleet that the attack will proceed.

Otto is summoned to the consulate and asked to devise a signaling system for US fleet movements. On November 28, he drives to Pearl Harbor with nine-year-old Hans and notes which ships are docked. He then develops an overly elaborate system of signals and presents his plan on November 30, but Kita tells him to simplify it.

On December 2, Otto and Friedel drive to the consulate with Christmas shopping as cover. Otto delivers the simplified plan to Okuda and provides a ship list. The codes are transmitted to Tokyo on December 3. The signals only cover movements through December 6, indicating an imminent attack.

On December 5 and 6, the consulate sends final ship counts and defense updates. On the afternoon of December 6, the consulate staff begins burning sensitive documents. Yoshikawa conducts a final reconnaissance and sends a transmission detailing the ships currently at anchor; this information is relayed to Vice Admiral Chuichi Nagumo’s approaching fleet. That night, Otto, Friedel, and Eberhard go to see a movie while Hans stays home.

At 6:00 am, 183 Japanese planes launch from aircraft carriers in rough seas. The attack commander uses Honolulu radio station KGMB to navigate to the island. At 7:02 am, a US radar site detects incoming planes, but they are assumed to be friendly B-17s.

At 7:45 am, Otto takes Hans to Sunday school while Friedel and Eberhard remain at home. Friedel hears approaching planes and assumes that it is merely an exercise, but the aircraft soon swarm over the house as nearby Kaneohe air base is attacked. At 7:53 am, the flight commander transmits a prearranged success signal. At 7:55 am, the Pearl Harbor attack begins.

Multiple battleships are destroyed. At 8:09 am, the USS Arizona explodes catastrophically, killing 1,500 men. Friedel, Eberhard, and their live-in servant, Hatsumi, listen to the radio as broadcaster Webley Edwards announces that the attack is real. Otto hears the news, rushes back to retrieve Hans from the church, and drives home through the chaos.

Special Agent Shivers orders the Japanese consulate surrounded. Civilian casualties occur from errant anti-aircraft shells. Shivers moves his wife, Corinne, and their adopted daughter, Sue, to safety as armed vigilantes hunt for Japanese Americans. When the 90-minute attack ends, over 2,400 are dead and the Pacific Fleet is in ruins.

FBI and police storm the consulate, arresting staff who are burning documents. Agents recover a stack of telegrams, including one detailing Otto’s signaling system. The Kuehns take shelter at a Red Cross station, where Eberhard is horrified by the grisly sight of the wounded. They return home as martial law is declared, and soon, Shivers, Burns, and Colonel George Bicknell begin ordering arrests of identified suspects. A mandatory blackout is enforced amid rumors and false alarms.

Shortly after midnight on December 8, FBI agent Ernest Halford arrives at the Kuehn home to apprehend the family. Eberhard is awakened by his mother’s screams and finds an armed agent in the living room. Halford handcuffs Otto, Friedel, and 15-year-old Eberhard, leaving nine-year-old Hans with the servants.

A search reveals high-powered binoculars, military clippings, photos, a shortwave radio, and an address book with suspicious German contacts. Agents then arrest Ruth at her Lanikai Beach house. Her husband, Jacob Moore, does not protest, instead telling agents that he has been suspicious of her and is relieved by her arrest. During the arrests, authorities find thousands of dollars in cash—taped to Friedel’s body and sewn into Ruth’s curtains—part of which is traced to the October Yoshikawa payment.

The family is taken to the detention center at the Honolulu immigration station, where they are strip-searched and separated. After three days, the telegram detailing Otto’s signal plan is decoded; it specifically mentions the Kalama dormer window. Agents confirm that the Kuehn house is the only one in Kalama with such a window.

The chapter flashes forward to the year 2010, when the author, Christine, learns from family friend Peter Wolfgang Becker that Ruth has died. Peter gives Christine a box of Ruth’s belongings. Inside is an address book with the K section ripped out, but Peter provides the hidden pages. 

Reinvigorated by the prospect of discovering more relatives who may have new information, Christine resumes her investigation. In response to her inquiries, she soon receives a Facebook response from Winnie Kuehn, the son of her uncle Hans, Eberhard’s younger brother. Winnie reveals that Ruth had cut off contact after Winnie asked questions about the family’s past.

The narrative returns to the aftermath of the Pearl Harbor attack. As the populace’s panic turns to rage, arrests of suspected enemy aliens continue for days. Most detainees, including the Kuehns, are sent to an internment camp on Sand Island, a barren coral spit surrounded by barbed wire and guard towers.

Shivers personally interrogates 15-year-old Eberhard, who insists that he knew nothing of his parents’ activities. Despite this, Shivers writes a memo classifying Eberhard as a dangerous national security threat who must remain detained. On the boat back to Sand Island, Eberhard is transported alongside Ensign Kazuo Sakamaki, the captured captain of a Japanese “midget” submarine and the first POW after the attack. Sakamaki had failed to infiltrate Pearl Harbor, and after his attempt to scuttle his sub failed, he swam to shore and was captured. Distraught and ashamed at being taken alive, Sakamaki tortures himself with cigarettes in captivity and begs to die by suicide. Eberhard is disturbed to be classified as an enemy like Sakamaki.

The harsh Sand Island conditions include floorless tents, rain, and a lack of basic amenities. Robert Shivers fights Hoover and Roosevelt’s plan to intern the entire Japanese population of Hawaii, influenced by his warm relationship with his “adopted daughter,” Sue. His stance contrasts with the mass internment of 120,000 Japanese Americans on the mainland.

While most internees are innocent, the Kuehns face public anger and federal prosecutors who are determined to convict them.