And the clue, the little fact that didn’t fit, was the increased slippage. The increased slippage that hadn’t happened on Verity’s drop, that should have prevented her from rescuing the cat, from committing the incongruity in the first place. Five minutes either way would have done it, but instead there’d been nine minutes’ worth. Nine minutes that had put her right at the scene of the crime.

“Every one of the simulated incongruities has increased slippage at the site,” T.J. had said. Every single one of them. Even the ones in which the incongruity was too great for the continuum to correct it. Every single one. Except ours.

And all we had was a cluster of slippage in 2018, which T.J. had said was too great for being that far from the site. And Coventry. Which was a crisis point.

“Ned,” Verity said urgently. “What’s wrong?”

“Shh,” I said, holding onto her arms like I had held onto the green metal uprights of Merton’s pedestrian gate. I almost had it, and if I didn’t jar it with any sudden movements or distractions, I would see the whole thing.

The slippage was too far from the site, and discrepancies were only found in the immediate vicinity of the incongruity. And the fur-bearing lady in Blackwell’s had said, “I’m glad she married him.” She had been talking about some woman who had married a farmer. “If she hadn’t, she’d still be trapped in Oxford, serving on church committees and running jumble—”

“Ned?” Verity said.

“Shh.”

“She was convinced the bishop’s bird stump had been stolen,” Carruthers had said, talking about the “bitter old spinster sort,” Miss Sharpe, who had been in charge of the Flower Committee.

And the ARP warden had said, “Come along, Miss Sharpe,” to the gray-haired woman guarding the west door. The gray-haired woman who had reminded me of someone, and she had said, “I have no intention of going anywhere. I am the vice-chairman of the Cathedral Ladies’ Altar Guild and the head of the Flower Committee.”

“Miss Sharpe,” he had called her.

Miss Sharpe, who had been so upset she’d accused everyone of knowing about the raid in advance. Who’d even written a letter to the editor.

She’d sent a letter to the paper, saying someone had advance knowledge of the raid.

In Coventry, which had known about the raid in advance. Which, unlike Muchings End, wasn’t an historical backwater. Which was a crisis point. Because of Ultra.

Because if the Nazis found out we had their Enigma machine, it could change the course of the war. The course of history.

And the only instance of something being brought forward through the net was as part of a self-correction.

I was gripping Verity’s arms so hard it had to be hurting her, but I didn’t dare let go. “That young woman in the cathedral,” I said. “What was her name?”

“In the cathedral?” Verity said bewilderedly. “Ned, there wasn’t anyone in the cathedral. It was on fire.”

“Not during the raid,” I said. “The day we went there with Tossie. The young woman who came to see the curate. What was her name?”

“I don’t… It was a flower name,” she said. “Geranium or—”

“Delphinium,” I said. “Not her first name. Her last name.”

“I… it began with an ‘S.’ Sherwood, no, Sharpe,” she said, and the world shifted 180 degrees, and I wasn’t at Balliol’s gate, I was on Merton’s playing fields, and there, in Christ Church Meadow, was Coventry Cathedral, the center of it all.

“Ned,” Verity said urgently. “What is it?”

“We’ve been looking at this the wrong way round,” I said. “You didn’t cause an incongruity.”

“But — the coincidences,” she stammered, “and the increased slippage in 2018. There had to have been an incongruity.”

“There was,” I said. “And, thanks to my amazing little gray cells, I know when it happened. And what caused it.”

“What?”

“Elementary, my dear Watson. I will give you a clue. Several clues, in fact. Ultra. The Moonstone. The Battle of Waterloo. Loose lips.”

“Loose lips?” she said. “Ned—”

“Carruthers. The dog that didn’t bark in the night. Penwipers. Pigeons. The least likely suspect. And Field General Rommel.”

“Field General Rommel?”

“The battle of North Africa,” I said. “We were using Ultra to locate Rommel’s supply convoys and sink them, being careful to send out a reconnaissance plane to be seen by the convoy so the Nazis wouldn’t get suspicious.”

I told her about the fog and the plane being unable to find the convoy, the RAF and the Navy’s simultaneous arrival, and about what Ultra had done afterward — the telegram, the planted rumors, the messages intended to be intercepted. “If the Nazis had found out we had Ultra, it would have changed the outcome of the war, so they had to set in motion an elaborate intelligence mission to correct the slip-up.” I beamed at her. “Don’t you see? It all fits.”

It all fit. Carruthers being trapped in Coventry, my making Terence miss meeting Maud, Professor Overforce pushing Professor Peddick in the Thames, even all those bloody jumble sales.

The fur-bearing ladies in Blackwell’s, Hercule Poirot, T.J., Professor Peddick with his talk of the Grand Design, all of them had been trying to tell me, and I’d been too blind to see it.

Verity was looking worriedly at me. “Ned,” she said, “exactly how many drops have you had?”

“Four,” I said. “The second of which was to Blackwell’s, where I overheard three fur-bearing matrons having an extremely enlightening discussion of a mystery novel, and the first of which was to the lab in 2018, where I heard Lizzie Bittner say she would do anything to keep Coventry Cathedral from being sold to a gaggle of spiritualists.”

The net began to shimmer faintly.

“What if there was an incongruity?” I said. “A slip-up? And the continuum, trying to protect the course of history, set in motion a sophisticated system of secondary defenses to correct the problem? Like Ultra, sending out telegrams and false leads, implementing an elaborate plan involving the drowning of cats and séances and jumble sales and elopements. And dozens of agents, some of whom weren’t even aware of the true purpose of the mission.”

The peonies glittered brightly. “In the best detective tradition, I cannot prove any of this,” I said. “Therefore, Watson, we must go collect evidence.” I picked up Verity’s bags and deposited them next to the peonies. “ ‘Quick, Watson! A hansom cab!’ ”

“Where are we going?” she said suspiciously.

“To the lab. 2057. To check the Coventry local papers and the cathedral’s committee rosters for 1888 and 1940.”

I took her arm, and we stepped into the shimmering circle. “And then,” I said, “we will go to get the bishop’s bird stump.”

The light began to grow. “Hold on,” I said and stepped out of the net to get the carpetbag.

“Ned!” Verity said.

“Coming,” I said. I opened the carpetbag, took out the boater, shut the bag and carried it back into the circle. I set the bag down and put the boater on at a jaunty angle that would have made Lord Peter proud.

“Ned,” Verity said, stepping back, her greenish-brown eyes wide.

“Harriet,” I said, and pulled her back into the already shining net.

And kissed her for a hundred and sixty-nine years.