“How, may I ask, did you know there was a back-up system?” The engineer was trying to keep calm, but his patience was being tested.

“Because I designed it, of course!”

• • •

“All the levels are the same layout, so it can’t be on any of the levels,” Vardy said.

“That doesn’t make any sense. You are sure the lab is on this base?”

“Ewan, I’ve been in and out of this place enough times, I’m hardly likely to confuse it with somewhere else!”

Jake sat down on the floor, his back against the wall. He was feeling weaker than ever, and the frayed tempers of those around him weren’t making matters any better.

“Jake? You alright? Here, drink some more water. That gas is dehydrating you.” Eric handed him a clear plastic bottle. He sipped at the liquid, not really thirsty, but not wanting to appear ungrateful.

“Russell, take us through how you got taken to the lab again. From the top,” Jake said, rubbing the palms of his hands into his eyes.

Vardy sighed, irritated at having to repeat himself. “I would go to the personnel entrance, the one we came through. My escort would take me to the lifts, we’d get in, they’d block the lift so nobody else could call it, then they would put the blindfold on. The lift went down. When we got out, we walked for a few minutes. It felt like we were going round in circles. I assume that was to throw me off. Then they took the blindfold off, and there I was, in the lab.”

“Did everyone get blindfolded?”

“All except Doctor Marshall. He was in charge of the lab. He came and went freely. Everyone else I worked with was on secondment from somewhere. None of us had clearance to know where exactly the lab was located.”

“Sounds like overkill. We’re all on the same side. What did they think they were hiding?” Eric muttered, shaking his head.

“I thought so too, to start with. The more I saw in that lab though, the more I understood. There were some horrific things under development. One lab assistant wanted out; she couldn’t deal with it. Imagine if she had decided to make trouble, to talk to others about the programme, or worse, the press. She would never have been able to prove a thing, because she would never be able to find the lab. The whole programme was off the record, deniable.”

“This isn’t helping us find it,” Jake said. “Are you sure the lift went down? Could it have gone up? Could the lab have been on the surface?”

“No, it went down. Deep down.”

“Hang on.” Ewan’s face lit up. “You said they blocked the lift so nobody could get in. Did they do that with a key?”

“Yes. The escort had a key, on a chain attached to his belt. How did you know?”

“In the apartment block where I lived, there’s a sub-basement. It’s where the heating systems are. They don’t want anyone going down there. The only way to access it is by putting a key into the control panel in the lift.”

Jake looked up. He understood at once. “That’s what your escort was doing! Ewan’s right. There must be another level, a hidden level, one you can only get to with the key!” He scrambled to his feet. “We have to go to the lifts!”

“Hold your horses,” Vardy said, sticking a hand in the air. “You could be right, it makes sense, a deeper level makes sense. But the lifts need power, and in case you hadn’t noticed, there isn’t any.” He spun his torch in his hand to underline the point. “And quite apart from that, we don’t have the key.”

“No, but the lift shaft must go down there, right, Jake?” Eric said, smiling.

Jake nodded. “We don’t need the lift, we just need to climb down the hole.”

• • •

The atmosphere in the engine room had changed considerably. Panic and fear had given way to a mix of relief and confusion. Relief because the battery meters had returned nearly all the way to their normal level. The immediate crisis had been averted; there would be no explosion. Confusion because after locating and starting the emergency cooling system, this strange old man had then begun connecting up the power supply from the Ambush. He whistled while he worked, and seemed annoyed by the questions Gunson and Lucya were throwing at him.

Gunson, for his part, had jumped in and was assisting in the task of getting the power back on. And despite his role as chief engineer on a Royal Navy submarine, it seemed clear to all three that Gunson was helping, and it was Tom Sanderson who was in charge.

“So you’re telling us,” Lucya said, pacing again, “that you not only designed the emergency cooling system for this ship, but you designed the whole engine room?”

“No, dear, that would be far too big a job for one man, even me. I was part of the design team, one of four.”

“How much of the room? Just the space? Or the engines too?”

“Oh no, I am no engine designer. But I did specify the diesel generators. And the battery backup system, and some ancillary systems too.”

“So you worked for Pelagios Line?”

“No, they were the client. I worked for the ship builder. All my working life. Started there as an apprentice when I was thirteen years old. Young people these days, they have it easy. Do you know, my granddaughter is twenty six and she is still in full-time education?” He stopped what he was doing, his eyes glazed over. “Was in education. I suppose she must be dead now. Terrible business. Terrible.” He gazed into space for a while, then abruptly turned and got back to the job in hand. “Still, there is nothing to be gained by mourning the past. What’s done is done, nothing we can do to change that.”

“Mr Sanderson, how come you didn’t mention any of this on your census form? If you had mentioned your expert knowledge of this ship, it would have been picked up by one of the people vetting the forms. You should be on the list of essential personnel.”

“Census? Pah! Lovely girl came to see me, I remember that. We had tea and biscuits. Don’t tell anyone will you, I kept a stash in my cabin!” He grinned cheekily, even looked a little bashful for a split second. “She asked me my profession, I told her I was retired. She asked from what, I said from design. That was that.”

Lucya stopped pacing and stared at him. “You didn’t think it was important to mention you designed part of this ship? You do understand the situation we are all in, Mr Sanderson?”

“There are plenty of very good engineers working on this ship. You don’t need an old codger like me getting in the way. And besides, I took my retirement years ago. I want to spend my time travelling the world. I spent all my working life making boats that other people could enjoy, and never once did I get to sail on one. This is my first trip, and I want to make the most of it. I have no intention of returning to work now, dear. Mr Gunson, could you pass me that green cable? If we get this done quickly enough you could come and join our little bingo game.”

• • •

“Come on, boys, give it some welly!” Vardy cried, punching the air with clenched fists, willing Eric and Ewan on as they tried to force open the lift doors. “That’s it, they’re opening!”

But no sooner had the doors been prised apart, than they sprang back shut.

“Argh, it’s no good.” Ewan fell back, landing on his bottom. The broom handle he had been using as a lever clattered to the floor. “Those things must be spring loaded, it’s ridiculous!”

“It’s a safety feature; they’re fire doors,” Eric confirmed. “We need something to hold them open.”

“Wait there, I know exactly what we can use,” Jake said. He jogged back down the corridor, looking for one of the many offices he had discovered. Inside he found what he was looking for, loaded himself up, and walked back to the lift at the briskest pace he could manage given his impaired breathing.

“Books?” Vardy looked at him sideways.

“Books,” Jake said. “Guys? Give it another go.”

Ewan scrambled to his feet, collected the broom handle and pushed it between the sliding doors. Eric did the same, the two of them facing each other.