The woman had finally made up her mind and paid. Polly stepped up to buy her guidebook. "Three pence," the volunteer said, and Polly reached into her purse for the coins, but her hands were so stiff with cold, she dropped them. They made an unholy, echoing clatter on the marble floor.

Well, thought Polly, if the retrieval team is here, this is one way to get their attention, but no one turned around.

"Sorry," she said, gathering up the coins and paying for the guidebook.

The volunteer handed it to her. "I'm afraid the Crypt and the choir are closed today."

The choir? Polly thought, wondering why, but asking would mean continuing to stand there in the draft from the windows.

She thanked the volunteer and walked up the nave. No one approached her, and she didn't see anyone who seemed to be there to meet someone. Several people knelt praying in the middle of the nave. Two Wrens stood in front of the bricked-up Wellington Monument, looking puzzledly up at it, and a pair of soldiers stood a few feet away, looking at the Wrens.

Just past the next pillar, a young woman stood, wearing a pair of open-toed shoes that looked like one of Wardrobe's bright ideas for an icy 1940 November and gazing around as though searching for someone. But before Polly could make her way around the chairs and across the nave to her, a member of the fire watch came up to the woman, and it was obvious from his smile, and hers, that they knew each other.

So clearly not the retrieval team, Polly thought. She turned to go see if anyone was in the transept. And nearly collided with a beaming Mr. Humphreys.

"I thought you'd come when you heard about our incident," he said. "We've had any number of people come to see the damage."

"Yes, it's dreadful about the windows," Polly said.

"It is," he agreed, looking back at them. "They should have been taken to Wales for safekeeping along with the other treasures. Still, it may turn out to have been a blessing in disguise. Sir Christopher Wren designed St. Paul's to have clear panes of glass in the windows, and now there is a good chance he will see his dream realized."

He would. At the end of the Blitz, there'd only be one intact window left in the entire cathedral, and that would be broken in 1944 by a V-1 that had exploded nearby, and all the replacement windows would be of clear glass.

"In the case of the altar, however," Mr. Humphreys went on, "I'm afraid it's another matter."

The altar?

"Luckily, the bomb damage was confined to it and the choir."

The choir. That's why the volunteer at the desk had said it was closed today.

Mr. Humphreys walked across the space under the dome and to the choir. The entrance was blocked off with a sawhorse. He moved it aside and led Polly through. "And the bomb went through to the Crypt, unfortunately just at the spot where our fire watch sleeps ..."

She wasn't listening. She was staring at the choir. And the destruction beyond.

Where the altar had been was a tumbled heap of timbers and shattered stone. Polly looked up. There was a gigantic jagged hole in the ceiling. A gray tarpaulin half covered it, water dripping from its edges onto a rickety-looking scaffold beneath.

But St. Paul's wasn't hit, she thought, staring unseeing at the gaping hole, at the rubble. It survived the war.

"When did this happen?" she demanded.

"The morning of October tenth, just as we were making one last round of the roofs. I was-" he said, and must have seen her face. "Oh, I am sorry. I thought from what you said that you knew. I should have prepared you. It gives one a shock, I know, seeing it for the first time."

Mr. Dunworthy hadn't said a word about a bomb hitting the altar. He'd spoken of the UXB and the incendiaries on the twenty-ninth of December, but nothing about an HE on October tenth. "The altar was entirely destroyed, and these two windows were broken," Mr. Humphreys explained.

"And the windows in the nave," Polly said. It hadn't been blast from a bomb the next street over which had broken them. It had been this bomb. Which Mr. Dunworthy had never mentioned.

"Yes. The bomb brought down more of the lower courses there." Mr. Humphreys pointed up at the edges of the hole. "Which hit the reredos. You can see where it's chipped, and where St. Michael's nose was broken off."

He went on, pointing out the damage, but she could scarcely hear him over the thudding of her heart. What if the reason Mr. Dunworthy hadn't told her about it was because it hadn't happened? Till now.

She'd persuaded herself there weren't any discrepancies, that the problem was increased slippage. Which was frightening enough. But this was even worse.

This is the proof that we've altered events, she thought.

"How bad is the damage to the structure?" she asked, afraid of the answer.

"Dean Matthews is hopeful the underlying supports weren't cracked," Mr. Humphreys said worriedly, "but we won't know till the engineers have completed their examination. The explosion lifted the roof off from end to end, and when it came down it may have damaged the supporting pillars."

In which case the blast from the bombs falling all around the cathedral on the twenty-ninth might bring the weakened pillars down, and St. Paul's with it. And what would that do to civilian morale? St. Paul's had been the heart of London. The photo of her dome standing firm above the fire and smoke had lifted the contemps' spirits and hardened their resolve for the remaining long, dark months of the Blitz. What would its destruction do to them? And to the outcome of the war?

"We were actually very lucky. It could have been far worse. The bomb struck the crown of the transverse arch and detonated in the space between the roofs. If it had hit farther down the apse or in the choir, or if it had fallen on through the roof before it exploded, the damage would have been far greater."

But this much damage may well be enough to alter the course of the war. I must write to Mike, she thought. He's got to get out of Bletchley Park.

"The organ case was badly damaged," Mr. Humphreys was saying. "Luckily, the pipes had been taken down to the Crypt for safekeeping-"

"I must go," Polly said. "Thank you for showing me the-"

"Oh, but I haven't shown you what the bomb did to the choir. Luckily, these pillars protected the stalls from-"

"Mr. Humphreys!" someone called. It was the firewatcher who'd been talking to the young woman with the open-toed shoes. He pushed past the barricade and came up to them. "Sorry to interrupt," he said, nodding to Polly, "but we need the duty roster, and Mr. Allen said you had it."

"You're busy," Polly said, taking advantage of the interruption. "I mustn't keep you. Goodbye." She walked quickly away.

"I gave it to Mr. Langby," she heard Mr. Humphreys say as she squeezed past the barricade.

Polly hurried down the nave and out of the cathedral. It had stopped raining, but she scarcely noticed, she was so intent on getting home and writing to Mike.

I hope Eileen's not there, she thought, and only then remembered she'd promised to meet her.

She glanced at her watch to see if she had time to go home, write the letter, and come back, but it was after two. The concert would be nearly over. And if I'm not there, she'll know something's wrong.

And she might know if it's truly a discrepancy or not, Polly thought. She said Mr. Dunworthy spoke to her about St. Paul's. He may have told her about the altar's being hit. If it was hit.

But it could easily have been hit without my knowing about it, Polly tried to persuade herself. The tenth of October would have been when she was preoccupied with Marjorie, not with reading newspapers, and before she'd gone to the morgue to look for her own death notice.

Or the bombing might not have been in the papers, given St. Paul's vital importance to the war, she thought, heading for the tube station. They wouldn't have wanted the Germans to know about it.

She reached Trafalgar Square just as the concert was letting out. Concertgoers were streaming out the doors and onto the porch where she'd seen Paige standing on VE-Day eve, buttoning coats and pulling on gloves, holding their hands out to see if it was raining, opening umbrellas.

Polly looked for Eileen. She was standing off to one side. Her face looked drawn and worried, and she'd wrapped her black coat tightly about her. The National Gallery must have been as frigid as St. Paul's.

"Eileen!" Polly called, and hurried across the wet square, the pigeons scattering before her, flying up to perch on the lions at the base of the monument.

Eileen saw her and raised her hand in recognition, but she didn't wave. Or smile. Polly glanced at her watch. It wasn't that late, and the concert had obviously just let out. And Eileen was always so cheerful and optimistic. Some of Polly's anxiety these last few weeks must have infected her.

Perhaps I shouldn't say anything about St. Paul's, she thought. It will only make things worse.

But Polly had to know. And there was no one else to ask. She ran up the steps and over to Eileen. "I need to ask you something," she said urgently. "Was St. Paul's-?"

But Eileen cut her off. "The retrieval team didn't come to the concert," she said. "Did you find them?"

"No, there was no one at St. Paul's."

"No one?" Eileen said, and there was an edge to her voice. Was she angry at her for insisting she go to the concert? If she was, it couldn't be helped. There were more important matters at hand.

"No historians at all?" Eileen persisted.

"No, and I was there from nine o'clock on. Eileen, do you know if St. Paul's was hit by any HEs during the Blitz?"

She looked surprised. "Hit by HEs?"

"Yes. Not incendiaries, high-explosive bombs. Did Mr. Dunworthy say anything about its being hit?"

"Yes," Eileen said. "But you-"

"Did he say when and which part of the cathedral?"

"I don't know all the dates. A UXB landed under the-"

"I know about the UXB. And the twenty-ninth."

"And the altar was hit on October tenth."

Thank God, Polly thought. It was supposed to have been hit.

Eileen was frowning. "If you were at St. Paul's this morning, then you saw the damage, didn't you?"

Oh, no. In her anxiety about the bombing, she'd totally forgotten Eileen knew nothing about her and Mike's fears that they'd altered events. "Yes, I mean, I did see it," she stammered, "but I didn't know ... Mr. Dunworthy had told me all about the UXB and the incendiaries, but not about the altar, and when I saw it, I-"

"Thought it might have happened this morning?"

This morning? What did that mean? But at least Eileen hadn't guessed the real reason she'd asked all these questions. "No, last night," Polly said. "And there was so much damage, it looked like the entire thing could collapse any minute, and even though I knew St. Paul's had survived, I thought ... I mean, I wasn't thinking. It was such a shock, seeing it. I hadn't realized St. Paul's had ever been hit by an HE."

"Two," Eileen said.

Two? Mr. Humphreys had said one.

"The other one was in the transept," Eileen said. "I don't know when."

"The north transept?" Polly asked, thinking irrelevantly of the memorial to Captain Faulknor. Mr. Humphreys would be so upset if that was destroyed.

"I don't know which transept. Mr. Bartholomew didn't say."

Mr. Bartholomew? Who was Mr. Bartholomew? Had someone here at the concert told her about the bombing of the altar? If so, then it could still be a discrepancy.

"Mr. Bartholomew?" Polly asked.

"Yes, John Bartholomew. He gave a lecture about it when I was a first-year."

Oh, thank goodness, it was someone from Oxford. "He's a professor at Balliol?"

"No, an historian. He gave a lecture about his experiences on the St. Paul's fire watch during the Blitz."

"He's here?" Polly grabbed Eileen's arms. "Why didn't you say something?"

"No, he's not here now. He was here years ago."

"In the Blitz. In 1940," Polly said, and when Eileen nodded, "It doesn't matter when he was here Oxford time. This is time travel. If he was here in 1940, he's still here now."

"Oh!" Eileen clapped her hand to her mouth. "I didn't even think of that! Is that why you-?"

"How could you not think of it?" Polly burst out. "Mike asked us to try to think of any past historians who might be here," she said, but even as she said it, she thought, That was that day he came to Townsend Brothers, before he left for Beachy Head, and Eileen wasn't there. And immediately after that, all their attention had turned to Bletchley Park.

"Mike never said a word to me about past historians," Eileen said defensively. "How-?"

"It doesn't matter. Now that we know he's here-"

"But he's not. He was injured when the bomb fell on the altar and went back to Oxford."

"How long after the bombing?"

"The next day."

Which meant he'd gone back two weeks before Mike had found her and the two of them had found Eileen.

"Oh, if I'd only realized," Eileen lamented.

"It wouldn't have made any difference," Polly said, sorry she'd upset her. "By the time we found one another and realized there was something wrong with our drops, it was already too late. He was already gone. You're certain he went back on the eleventh?"

"Yes. I don't remember very much about the lecture because it was on 1940, and the only part of World War III wanted to go to at that point was VE-Day-"

So you didn't pay attention, just as you didn't pay attention to Gerald, Polly thought bitterly. But that was unfair. Eileen could scarcely be expected to know that three years later the details of a first-year lecture would prove to be vitally important.

"-but I do remember Mr. Bartholomew talking about going back the morning after St. Paul's was attacked," Eileen went on. "Because I assumed it was because he was injured and needed medical attention."

Like Mike, Polly thought. Only no one had come to pull him out. "I don't suppose he said where his drop was, did he?"

"No. But if he's gone back, his drop wouldn't be working now, would it?"

It might, Polly thought, but she couldn't tell Eileen that or she might begin questioning Polly about her earlier assignments. Might his drop have been in St. Paul's?

No, not with people there all day and the fire watch there at night. She wondered suddenly if John Bartholomew had been in the cathedral that first day she'd gone there. He might very well have been that firewatcher she'd seen coming on duty as she left. Or one of the men out by the UXB.

If I'd known he was there, I could have gone back to St. Paul's and told him I was in trouble as soon as I found out my drop wouldn't open, she thought, and he could have got word to Mr. Dunworthy ...

"Would it?" Eileen was asking. "Still be working? Mr. Bartholomew's drop? I thought drops shut down when the historian returned and the assignment was over."