"Take the baby," John demanded, lifting Maisie and putting her into Sherlock's arms whether he wanted her or not. It took a dazed second for Sherlock to realise why. From below deck, he could no longer hear Sadie's ragged breathing.

"What-"

"Hypothermic," John barked, already halfway down the galley stairs. Sherlock followed him to the top of the shaft. "But she's breathing and she's got a pulse, so unless that changes you don't need to resuscitate her-"

"But what do I do with her?"

"Sherlock, I'm about to be really, really busy, so please, use your common sense." Looking down the ladder into the galley, Sherlock saw that John was kneeling over something. Someone. "Her clothes are wet," he said over his shoulder. "Get them off her. Get her warm."

Somewhere out in the darkness, Donovan was shouting for Dyer. Only she was calling him Jake. And he wasn't answering.

"Dyer," tumbled out of Sherlock's mouth. "They can't find him-"

"I can't do anything about that now." John was taking Sadie's pulse at the neck and fumbling to get his jacket off to free his arms. "There's help on the way. You just keep that kid warm, okay?"

"But-"

"Sherlock, Dyer's got two working arms and legs and he went into the water voluntarily. You're holding a two-year-old who's in a hypothermic coma. Dyer can't be your priority right now."

With numb fingers, Sherlock stripped Maisie of her wet, filthy clothes. As he did so, he heard a sickening crack from down in the cabin. John was attempting chest compressions, and had just broken at least two of Sadie Holland's ribs. He suddenly wondered, for the first time since meeting him, whether people had died because the world held only one John Watson.

Maisie was still unconscious. His instinct was to get her out of the freezing night air; but with Sadie sprawled out on the cabin floor and John trying to resuscitate her, there was no room to take her down there. He took off his coat, jacket and shirt, bundled Maisie close to his chest, and awkwardly put them on again with his free hand. Her skin was icy against his, and her head flopped against his shoulder like a rag doll's. He could still dimly see Lestrade, Donovan and Derrick huddled together in the water a few dozen yards off, but it was not his imagination—they were further away now. The tide was on its way out.

Then, from the port bow, he heard a splash. Still clutching Maisie, he rushed over, peering down at the vague, sopping form flailing and gasping at the waterline.

"Dyer?"

Donovan called out again. Sherlock ignored her. So far, both she and Lestrade had the common sense not to swim against the tide to find their missing constable. If they knew where he was, Sherlock was sure that Donovan would try. Exhausted swimmers drowned.

Dyer was scrabbling for purchase against the fibreglass hull, pressed against it by the undertow. The swell broke over his head. Sherlock, cradling Maisie against him with his free arm, found the mooring rope and threw it over. "Hold that," he said. "Can you hold it?"

Dyer gripped it and started tying it around one wrist. The swell slapped him in the face, leaving him gasping. "The rope," he puffed. "How long is it?"

Sherlock glanced back at the coil on the deck. "Forty feet," he said. "Maybe fifty. But you-"

It was too late. Dyer had submerged again, and this time it was deliberate. The line began to pull, and Sherlock, still holding onto the unconscious baby, was left waiting in agony until he dimly saw Dyer remerge a few feet away from Donovan.

He counted out his heartbeats against the crash of waves on the dwindling shoreline.

In his arms, Maisie suddenly stirred and made a shallow barking sound. He tilted her forward, looking at her face; she was screwing her swollen eyes up and puffing breaths through her mouth.

"Come on," he muttered, laying her freezing little body against his shoulder and patting her back, the way he'd seen both John and Molly tend their daughter a thousand times. He hadn't the faintest idea if it was doing anything to help, but surely it wasn't doing anything to hurt. He pulled her forward to look at her face again when he heard Lestrade's voice out on the water, hoarse and cross.

"Not me," he was saying. "Her."

A choked protest from Donovan. "Boss-"

"Nicely spotted. Her, Dyer."

For a moment, Sherlock fought off a fit of hysterical giggling. The Met's finest, treading water in the Atlantic, bickering over which one of them deserved the mooring rope. He heard a slapping noise, and a pale spray of water flared up between Lestrade and Donovan, very near Derrick Rice's head. "Hey," Lestrade barked. "Bite me again and you'll bloody know it!"

"I'll pull you in," Sherlock called, stooping awkwardly under Maisie's deadweight to pick up the rope again. Maisie coughed into his chest, a full-bodied shudder followed by a whooping intake of breath. It was echoed down in the cabin, where John was still trying to resuscitate Sadie. In between breaths, Sherlock could hear John muttering Come on, Sadie…

For a second, Sherlock thought he caught a high-pitched moan in response. But it wasn't Sadie; it was the sirens of an ambulance rounding the northern corner of the promenade and winging in a heavy curve toward the marina. Red and blue lights flashed out from the shore. Maisie bunched her tiny hands into fists and set up a gurgling cry.

For reasons beyond the comprehension of Sherlock Holmes, McMannis and the rest of the Cornwall officers on the scene weren't particularly interested in hearing the details on how Sherlock Holmes had solved the mystery of the Marie Celeste. Two ambulances left the scene almost immediately, with Sadie and Maisie inside them, while they waited an extra two minutes for a third to arrive and tend to Derrick Rice. So far as Sherlock's observations went, he'd gone into the ambulance both alive and conscious. Like many self-inflicted throat wounds, his had been barely deeper than superficial. There had been, he told McMannis, no real reason for all three Met detectives to jump in the freezing Atlantic after him.

Behind him, one police officer in uniform called out to another. He looked over his shoulder, then went back to another ambulance, which had arrived in the last few minutes. There, Lestrade, Donovan and Dyer were waiting to be given the all-clear to leave without further medical attention. Someone had come up with dry clothing for them; Dyer was wearing a grey jumper that hung off his thin shoulders, and Donovan's shirt and jacket both clearly belonged to a man. Even soaking wet and wearing a random collection of clothing pulled from the back of one of the police vehicles attending, Greg Lestrade was, as ever, the picture of masculine dignity.

"Well," Sherlock said as he made his way over. "If nothing else comes of this case, the order in which you jumped off that wall was illuminating."

"Yeah, thanks for that, guys," Donovan said through chattering teeth. "I really enjoyed that, and all for someone like Derrick Rice. Still. Better a conviction, or at least a trial, than another body."

"Yes." Sherlock put his hands in his pockets, glancing down at his shoes a second. "Quite right. Between Lestrade's first aid and the near-freezing water, Derrick Rice didn't even lose enough blood to pass out, let alone kill him. The court case is sure to be riveting."

"Great," Lestrade said. "And what about Sadie and Maisie?"

"John says…" Sherlock trailed off, looking around. He'd been about to say 'John says they're both too early to call', since that was the last thing he'd heard John say in the confusion of transferring Sadie and Maisie into the hands of the paramedics. But that had been a good fifteen minutes before, and he hadn't seen John since.

Lestrade gestured behind him, and Sherlock turned. In the darkness, he was just able to make out John a good fifty metres further north of the marina, sitting on the low curved wall that separated the road and the beach. Sherlock's first assumption was that he had wandered away to make a phone call, but there was nothing in his hands.

He looked back over his shoulder at Lestrade, who was just then accepting a bright-green mug of something hot from one of the paramedics.

Putting his freezing hands in his coat pockets, he strolled along the wall toward John, who looked up as he approached but neither spoke nor got up. It seemed wrong to sit down beside him, somehow, so he remained standing, looking out to sea, listening to the rhythmic crash of the ocean against the sea wall beyond them.

"Are you all right?" he finally asked, unable to think of any other meaningful remark.

"Yeah." John rubbed his forehead with two fingers. "Yeah, just needed a couple of minutes to recharge, you know, clear my head. CPR's tiring."

"Is Molly coming?"

John shook his head. "I told her to wait up at headquarters. No point in her coming down here—you, me, Greg… we're all fine."

"Yes." Sherlock cleared his throat. "Yes, I suppose we are."

John glanced back at Lestrade, who had wandered away from the ambulance and was deep in conversation with McMannis, a forgotten blanket still draped over his shoulders. "They should give Greg a medal for this, you know," he said. "I'd have left Derrick to drown."

"You didn't see me jumping in after him," Sherlock pointed out.

"Life sentence, like Adrian said. They're not going to put Adrian in prison now, are they?"

Sherlock shook his head. "He's served his time for that," he said. "And I doubt Ethan will want to retry him, anyhow."

John made a low, bitter scoffing noise that warned Sherlock to go no further on the subject of Ethan Frost. He looked back over his shoulder, watching Dyer get up and make his way over to where Lestrade and McMannis were still talking. Donovan pulled her legs up to her body and curled up on her side, regardless of the cold stone slab she was lying against. A paramedic in a high-visibility jacket made a beeline for her and gave her a gentle shake, and she scowled and sat up again.

"God," John said, having just noticed the same thing. "Donovan looks like a half-drowned cat. I should go over and see if she's okay-"

"The paramedics are doing that," Sherlock pointed out. "You're off-duty."

"Doctors are never off-duty, Sherlock. You've known me how many years now?"

"I think you've acquitted yourself and your profession tonight. You just saved Sadie's life."

"Yeah, well. Maybe." John winced. "I kept her on standby until the ambulance arrived. No guarantees. If it comes to it, you saved Maisie's life. Anyway, I'm not the one who figured out where they were."

At this, Sherlock clenched his jaw, shoving both hands in his pockets. "I should have known," he muttered.

"You did know."

"I should have known days ago."

"Like you always say yourself," John said, standing up. "All puzzles are simple when you already know the solution. Come on. I need coffee. From the looks of her, I daresay your mistress could do with some, too."

"Oh, shut up," Sherlock snapped, but John was too busy laughing to take any notice.