Hermia Mount looked with dismay at her lunch - two charred sausages, a dollop of runny mashed potato, and a mound of overcooked cabbage - and she thought with longing of a bar on the Copenhagen waterfront that served three kinds of herring with salad, pickles, warm bread, and lager beer.

She had been brought up in Denmark. Her father had been a British diplomat who spent most of his career in Scandinavian countries. Hermia had worked in the British Embassy in Copenhagen, first as a secretary, later as assistant to a naval attache who was in fact with MI6, the secret intelligence service. When her father died, and her mother returned to London, Hermia stayed on, partly because of her job, but mainly because she was engaged to a Danish pilot, Arne Olufsen.

Then, on April 9, 1940, Hitler invaded Denmark. Four anxious days later, Hermia and a group of British officials had left in a special diplomatic train that brought them through Germany to the Dutch frontier, from where they traveled through neutral Holland and on to London.

Now at the age of thirty Hermia was an intelligence analyst in charge of MI6's Denmark desk. Along with most of the service, she had been evacuated from its London headquarters at 54 Broadway, near Buckingham Palace, to Bletchley Park, a large country house on the edge of a village fifty miles north of the capital.

A Nissen hut hastily erected in the grounds served as canteen. Hermia was glad to be escaping the Blitz, but she wished that by some miracle they could also have evacuated one of London's charming little Italian or French restaurants, so that she would have something to eat. She forked a little mash into her mouth and forced herself to swallow.

To take her mind off the taste of the food, she put today's Daily Express beside her plate. The British had just lost the Mediterranean island of Crete. The Express tried to put a brave face on it, claiming the battle had cost Hitler eighteen thousand men, but the depressing truth was that this was another in a long line of triumphs for the Nazis.

Glancing up, she saw a short man of about her own age coming toward her, carrying a cup of tea, walking briskly but with a noticeable limp. "May I join you?" he said cheerfully, and sat opposite her without waiting for an answer. "I'm Digby Hoare. I know who you are."

She raised an eyebrow and said, "Make yourself at home."

The note of irony in her voice made no apparent impact. He just said, "Thanks."

She had seen him around once or twice. He had an energetic air, despite his limp. He was no matinee idol, with his unruly dark hair, but he had nice blue eyes, and his features were pleasantly craggy in a Humphrey Bogart way. She asked him, "What department are you with?"

"I work in London, actually."

That was not an answer to her question, she noted. She pushed her plate aside.

He said, "You don't like the food?"

"Do you?"

"I'll tell you something. I've debriefed pilots who have been shot down over France and made their way home. We think we're experiencing austerity, but we don't know the meaning of the word. The Frogs are starving to death. After hearing those stories, everything tastes good to me."

"Austerity is no excuse for vile cooking," Hermia said crisply.

He grinned. "They told me you were a bit waspish."

"What else did they tell you?"

"That you're bilingual in English and Danish - which is why you're head of the Denmark desk, I presume."

"No. The war is the reason for that. Before, no woman ever rose above the level of secretary-assistant in MI6. We didn't have analytical minds, you see. We were more suited to homemaking and child-rearing. But since war broke out, women's brains have undergone a remarkable change, and we have become capable of work that previously could only be accomplished by the masculine mentality."

He took her sarcasm with easy good humor. "I've noticed that, too," he said. "Wonders never cease."

"Why have you been checking up on me?"

"Two reasons. First, because you're the most beautiful woman I've ever seen." This time he was not grinning.

He had succeeded in surprising her. Men did not often say she was beautiful. Handsome, perhaps; striking, sometimes; imposing, often. Her face was a long oval, perfectly regular, but with severe dark hair, hooded eyes, and a nose too big to be pretty. She could not think of a witty rejoinder. "What's the other reason?"

He glanced sideways. Two older women were sharing their table, and although they were chatting to each other, they were probably also half-listening to Digby and Hermia. "I'll tell you in a minute," he said. "Would you like to go out on the tiles?"

He had surprised her again. "What?"

"Will you go out with me?"

"Certainly not."

For a moment he seemed nonplussed. Then his grin returned, and he said, "Don't sugar the pill, give it to me straight."

She could not help smiling.

"We could go to the pictures," he persisted. "Or to the Shoulder of Mutton Pub in Old Bletchley. Or both."

She shook her head. "No, thank you," she said firmly.

"Oh." He seemed crestfallen.

Did he think she was turning him down because of his disability? She hastened to put that right. "I'm engaged," she said. She showed him the ring on her left hand.

"I didn't notice."

"Men never do."

"Who's the lucky fellow?"

"A pilot in the Danish army."

"Over there, I presume."

"As far as I know. I haven't heard from him for a year."

The two ladies left the table, and Digby's manner changed. His face turned serious and his voice became quiet but urgent. "Take a look at this, please." He drew from his pocket a sheet of flimsy paper and handed it to her.

She had seen such flimsy sheets before, here at Bletchley Park. As she expected, it was a decrypt of an enemy radio signal.

"I imagine I've no need to tell you how desperately secret this is," Digby said.

"No need."

"I believe you speak German as well as Danish."

She nodded. "In Denmark, all schoolchildren learn German, and English and Latin as well." She studied the signal for a moment. "Information from Freya?"

"That's what's puzzling us. It's not a word in German. I thought it might mean something in one of the Scandinavian languages."

"It does, in a way," she said. "Freya is a Norse goddess - in fact she's the Viking Venus, the goddess of love."

"Ah!" Digby looked thoughtful. "Well, that's something, but it doesn't get us far."

"What's this all about?"

"We're losing too many bombers."

Hermia frowned. "I read about the last big raid in the newspapers - they said it was a great success."

Digby just looked at her.

"Oh, I see," she said. "You don't tell the newspapers the truth."

He remained silent.

"In fact, my entire picture of the bombing campaign is mere propaganda," she went on. "The truth is that it's a complete disaster." To her dismay, he still did not contradict her. "For heaven's sake, how many aircraft did we lose?"

"Fifty percent."

"Dear God." Hermia looked away. Some of those pilots had fiancees, she thought. "But if this goes on . . ."

"Exactly."

She looked again at the decrypt. "Is Freya a spy?"

"It's my job to find out."

"What can I do?"

"Tell me more about the goddess."

Hermia dug back into her memory. She had learned the Norse myths at school, but that was a long time ago. "Freya has a gold necklace that is very precious. It was given to her by four dwarves. It's guarded by the watchman of the gods . . . Heimdal, I think his name is."

"A watchman. That makes sense."

"Freya could be a spy with access to advance information about air raids."

"She could also be a machine for detecting approaching aircraft before they come within sight."

"I've heard that we have such machines, but I've no idea how they work."

"Three possible ways: infrared, lidar, and radar. Infrared detectors would pick up the rays emitted by a hot aircraft engine, or possibly its exhaust. Lidar is a system of optical pulses sent out by the detection apparatus and reflected back off the aircraft. Radar is the same thing with radio pulses."

"I've just remembered something else. Heimdal can see for a hundred miles by day or night."

"That makes it sound more like a machine."

"That's what I was thinking."

Digby finished his tea and stood up. "If you have any more thoughts, will you let me know?"

"Of course. Where do I find you?"

"Number Ten, Downing Street."

"Oh!" She was impressed.

"Goodbye."

"Goodbye," she said, and watched him walk away.

She sat there for a few moments. It had been an interesting conversation in more ways than one. Digby Hoare was very high-powered: the Prime Minister himself must be worried about the loss of bombers. Was the use of the code name Freya mere coincidence, or was there a Scandinavian connection?

She had enjoyed Digby's asking her out. Although she was not interested in dating another man, it was nice to be asked.

After a while, the sight of her uneaten lunch began to get her down. She took her tray to the slops table and scraped her plate into the pigbin. Then she went to the ladies' room.

While she was in a cubicle, she heard a group of young women come in, chattering animatedly. She was about to emerge when one of them said, "That Digby Hoare doesn't waste time - talk about a fast worker."

Hermia froze with her hand on the doorknob.

"I saw him move in on Miss Mount," said an older voice. "He must be a tit man."

The others giggled. In the cubicle, Hermia frowned at this reference to her generous figure.

"I think she gave him the brush-off, though," said the first girl.

"Wouldn't you? I couldn't fancy a man with a wooden leg."

A third girl spoke with a Scots accent. "I wonder if he takes it off when he shags you," she said, and they all laughed.

Hermia had heard enough. She opened the door, stepped out, and said, "If I find out, I'll let you know."

The three girls were shocked into silence, and Hermia left before they had time to recover.

She stepped out of the wooden building. The wide green lawn, with its cedar trees and swan pond, had been disfigured by huts thrown up in haste to accommodate the hundreds of staff from London. She crossed the park to the house, an ornate Victorian mansion built of red brick.

She passed through the grand porch and made her way to her office in the old servants' quarters, a tiny L-shaped space that had probably been the boot room. It had one small window too high to see out of, so she worked with the light on all day. There was a phone on her desk and a typewriter on a side table. Her predecessor had had a secretary, but women were expected to do their own typing. On her desk, she found a package from Copenhagen.

After Hitler's invasion of Poland, she had laid the foundations of a small spy network in Denmark. Its leader was her fiance's friend, Poul Kirke. He had put together a group of young men who believed that their small country was going to be overrun by its larger neighbor, and the only way to fight for freedom was to cooperate with the British. Poul had declared that the group, who called themselves the Nightwatchmen, would not be saboteurs or assassins, but would pass military information to British Intelligence. This achievement by Hermia - unique for a woman - had won her promotion to head of the Denmark desk.

The package contained some of the fruits of her foresight. There was a batch of reports, already decrypted for her by the code room, on German military dispositions in Denmark: army bases on the central island of Fyn; naval traffic in the Kattegat, the sea that separated Denmark from Sweden; and the names of senior German officers in Copenhagen.

Also in the package was a copy of an underground newspaper called Reality. The underground press was, so far, the only sign of resistance to the Nazis in Denmark. She glanced through it, reading an indignant article which claimed there was a shortage of butter because all of it was sent to Germany.

The package had been smuggled out of Denmark to a go-between in Sweden, who passed it to the MI6 man at the British Legation in Stockholm. With the package was a note from the go-between saying he had also passed a copy of Reality to the Reuters wire service in Stockholm. Hermia frowned at that. On the surface, it seemed a good idea to publicize news of conditions under the occupation, but she did not like agents mixing espionage with other work. Resistance action could attract the attention of the authorities to a spy who might otherwise work unnoticed for years.

Thinking about the Nightwatchmen reminded her painfully of her fiance. Arne was not one of the group. His character was all wrong. She loved him for his careless joie de vivre. He made her relax, especially in bed. But a happy-go-lucky man with no head for mundane detail was not the type for secret work. In her more honest moments, she admitted to herself that she was not sure he had the courage. He was a daredevil on the ski slopes - they had met on a Norwegian mountain, where Arne had been the only skier more proficient than Hermia - but she was not sure how he would face the more subtle terrors of undercover operations.

She had considered trying to send him a message via the Nightwatchmen. Poul Kirke worked at the flying school, and if Arne was still there they must see one another every day. It would have been shamefully unprofessional to use the spy network for a personal communication, but that did not stop her. She would have been found out for sure, because her messages had to be encrypted by the code room, but even that might not have deterred her. It was the danger to Arne that held her back. Secret messages could fall into enemy hands. The ciphers used by MI6 were unsophisticated poem codes left over from peacetime, and could be broken easily. If Arne's name appeared in a message from British intelligence to Danish spies, he would probably lose his life. Hermia's inquiry about him could turn into his death warrant. So she sat in her boot room with acid anxiety burning inside her.

She composed a message to the Swedish go-between, telling him to keep out of the propaganda war and stick to his job as courier. Then she typed a report to her boss containing all the military information in the package, with carbon copies to other departments.

At four o'clock she left. She had more work to do, and she would return for a couple of hours this evening, but now she had to meet her mother for tea.

Margaret Mount lived in a small house in Chelsea. After Hermia's father had died of cancer in his late forties, her mother had set up home with an unmarried school friend, Elizabeth. They called each other Mags and Bets, their adolescent nicknames. Today the two had come by train to Bletchley to inspect Hermia's lodgings.

She walked quickly through the village to the street where she rented a room. She found Mags and Bets in the parlor talking to her landlady, Mrs. Bevan. Hermia's mother was wearing her ambulance driver's uniform, with trousers and a cap. Bets was a pretty woman of fifty in a flowered dress with short sleeves. Hermia hugged her mother and gave Bets a kiss on the cheek. She and Bets had never become close, and Hermia sometimes suspected Bets was jealous of her closeness to her mother.

Hermia took them upstairs. Bets looked askance at the drab little room with its single bed, but Hermia's mother said heartily, "Well, this isn't bad, for wartime."

"I don't spend much time here," Hermia lied. In fact she spent long, lonely evenings reading and listening to the radio.

She lit the gas ring to make tea and sliced up a small cake she had bought for the occasion.

Mother said, "I don't suppose you've heard from Arne?"

"No. I wrote to him via the British Legation in Stockholm, and they forwarded the letter, but I never heard back, so I don't know whether he got it."

"Oh, dear."

Bets said, "I wish I'd met him. What's he like?"

Falling in love with Arne had been like skiing downhill, Hermia thought: a little push to get started, a sudden increase in speed, and then, before she was quite ready, the exhilarating feeling of hurtling down the piste at a breakneck pace, unable to stop. But how to explain that? "He looks like a movie star, he's a wonderful athlete, and he has the charm of an Irishman, but that's not it," Hermia said. "It's just so easy to be with him. Whatever happens, he just laughs. I get angry sometimes - though never at him - and he smiles at me and says, 'There's no one like you, Hermia, I swear.' Dear God, I do miss him." She fought back tears.

Her mother said briskly: "Plenty of men have fallen in love with you, but there aren't many who can put up with you." Mags's conversational style was as unadorned as Hermia's own. "You should have nailed his foot to the floor while you had the chance."

Hermia changed the subject and asked them about the Blitz. Bets spent air raids under the kitchen table, but Mags drove her ambulance through the bombs. Hermia's mother had always been a formidable woman, somewhat too direct and tactless for a diplomat's wife, but war had brought out her strength and courage, just as a secret service suddenly short of men had allowed Hermia to flourish. "The Luftwaffe can't keep this up indefinitely," said Mags. "They don't have an unending supply of aircraft and pilots. If our bombers keep pounding German industry, it must have an effect eventually."

Bets said, "Meanwhile, innocent German women and children are suffering just as we do."

"I know, but that's what war is about," said Mags.

Hermia recalled her conversation with Digby Hoare. People like Mags and Bets imagined that the British bombing campaign was undermining the Nazis. It was a good thing they had no inkling that half the bombers were being shot down. If people knew the truth they might give up.

Mags began to tell a long story about rescuing a dog from a burning building, and Hermia listened with half an ear, thinking about Digby. If Freya was a machine, and the Germans were using it to defend their borders, it might well be in Denmark. Was there anything she could do to investigate? Digby had said the machine might emit some kind of beam, either optical pulses or radio waves. Such emissions ought to be detectable. Perhaps her Nightwatchmen could do something.

She began to feel excited about the idea. She could send a message to the Nightwatchmen. But first, she needed more information. She would start work on it tonight, she decided, as soon as she had seen Mags and Bets back onto their train.

She began to feel impatient for them to go. "More cake, Mother?" she said.