I stalked back through the city of cubes until I reached my office. It was a large glass container divided into two: Alex and I would be working in the smaller section while the rest of our team would work in the bigger one. The whole space was uncomfortably cool, and most officers next door kept their coats on.

Through the walls, I could see that Alex was sitting at Nina's old desk. It had been cleared of all her things now, and he obviously wasn't going to personalise it himself when he'd brought so little luggage.

I entered and crossed to my own space: the bigger desk that faced the rest of my team and had a tablet hovering in the air over it -- which I hadn't switched on for months. A couple of old paper coffee cups were sitting beneath it, daring it to fall and send them flying. I sat down and rested my elbows on the glass. "Found anything yet?"

"Ryker's robot alibi checks out. He left before the murder."

"Which means he doesn't really have an alibi. He could have returned later and killed Zoe in the alley."

"Yes." Alex scrutinised me in the same manner he'd scrutinised our suspects. "What did the chief super want to talk to you about?"

"Nothing to do with the investigation."

He took the hint and looked back at his tabphone, hovering at eye-level over his desk. "I'll check Zoe's Xplora page for anything useful."

Xplora was a social network. In fact, it was the social network. Run by the government, it was the only one in existence and the only way we could make phone calls or send messages. It was also where news stories were published, books were read, films were watched, and music was played. It was everything.

"Good idea," I said. "I'll start looking at Maxx's profiles."

His national profile turned up the basics. Maxx Ackerman. Twenty-four. Worked at Ackerman Electronics. Married to Zoe Ackerman. Daughter was Harley Ackerman. Mother was Elena Ackerman. His biological father had been a man named Philip Ackerman, but he'd died two decades ago.

I scanned through pages and pages of information, then spent a while looking for anything of interest on his Xplora page. There was nothing.

Alex broke the silence. "I've just pulled up Ryker James' national profile. He was charged with ABH in 2180 for a fight outside Victory Casino. His opponent shot him in the arm for his trouble."

ABH stood for actual bodily harm, the lowest statutory offence of assault. Perhaps that was how Ryker had come to have his cybernetic implant. "So, he has violent tendencies. Who was the arresting officer?"

"DI Flynn."

I was a little surprised, but that was something, at least. "Sebastian Flynn's a friend, so I'll ask if he can remember anything about Ryker when I next see him. And add looking through the report of the incident to my to-do list."

There was a knock on the door, and a plainclothes officer pushed it open: Detective Constable Emily Laney. She was carrying a small box which she brought straight to me. "Zoe Ackerman's possessions, ma'am, from the hospital."

"Thank you."

She left, and I tore the box open to examine the items Zoe had been carrying when she'd died. Compact mirror, electrode earphones, mints, tabphone. I pounced on the electronic device.

It was locked. I groaned.

"I can crack that." Alex appeared at my side and took the tabphone off me. I watched him without much hope, but a minute later it was back on my desk. He smiled at my bemused expression.

"Even Nina couldn't do that!" I said. "I thought I'd have to brave talking to the PRBs. How did you do it?"

He went back to his desk, a spark of mischief in his eyes. "It's an old skill. When I was at school, I thought it was funny to crack people's passwords and mess around with their tabphones."

I hoped that wasn't still a habit!

Zoe's tabphone had recorded ten missed calls, ranging from 7:15 a.m. to 8:47 a.m that morning. No messages had been left. All the calls had been made by Maxx Ackerman.

Why hadn't he rung as soon as he'd got home the previous night? Why hadn't he rung to apologise, or ask where she was?

And why did it look like she'd been intending to run straight into Ryker's arms when she'd died?

I met Alex's eyes across the office. Eyes that had already been fastened on me, and jostled my heartbeat with their intensity.

I gulped and shoved my chair back, surprised and unnerved. "Let's see what the rest of the Castle-Ackermans know."

***

If the newly-wed Ackermans had lived in another world, the Castle-Ackermans lived on another planet. They were based in the sort of skyscraper that had probably been featured on the news; the sort to have been made by someone who would now be very rich, but who was so unusual in their work and in themselves that their name would never be heard of again except for in the smallest, most eccentric circles.

I couldn't decide if it looked more like a squid, a worm, or an alien. Chunks of frosted glass and spindly metal twisted around the core -- if there was a core beneath it all -- sticking sharply up towards the sky at varying angles. In fact, the whole building seemed to constantly twist, bending and flexing and stretching, and it was hard to believe that any of the materials managed to support themselves. Or to imagine where on the writhing creature the entrance might be found.

Once we'd eventually got inside the squid-worm, it was deathly quiet. The ceiling towered hundreds of feet above us, and corridors for different levels crawled around the walls, supported by glass pillars like circular balconies. It was bright, much brighter than the outside world, and oddly, the lobby was filled with winter flowers and trimmed bushes to create an enormous indoor park. Grey mosaic walkways carved straight paths through the vegetation to lifts set into the walls. We followed one and tried not to gawp.

Again, our destination was the top floor, where the Castle-Ackermans owned a duplex. A large duplex, I realised when we stepped out of the lift and saw only one door to choose from. A PRB was standing on guard there. The door had been left open a crack, so we flashed our warrant cards at the robot and strode straight in.

The grey entrance hall stretched in three directions like a maze, but I could hear soft talking ahead where the walls fell back to create a wide, open room. We walked in that direction, the floor toasty beneath our shoes. Someone had cranked the heating up as high as they could get it.

We entered a combined living space: to the left was a kitchen the size of my flat, made up of slanting counters that defied gravity and a dark marble extractor fan. It was an asymmetric block that came down so low from the ceiling, it looked like a sinister chute that might abduct anyone unfortunate enough to be standing beneath it. The living room was less nightmarish, containing a string of white leather sofas, a glass TV, and a fake modern fireplace. The view on the windows was of a distant, frosted village from the surface.

A boy and a girl barely out of their teens were sitting in front of the TV, at opposite ends of the sofa. They had to be the younger siblings listed on Zoe's national profile: Jason and Lynn Castle-Ackerman.

Jason was another dark-haired handsome devil like his brother, although he had an oval face without such a prominent bone structure. Both he and Lynn also had a trace of Korean ancestors in their features, as Zoe had, but Lynn had spoiled her delicate beauty by dip-dyeing her hair a hideous shade of green. With the exception of her red-rimmed eyes, the rest of her was green, too -- baggy green jumper, green jogging bottoms, green socks -- so that it was like someone had spilled mushy peas on the sofa.

Only she was looking at us. I cleared my throat and waited until I had the attention of them both. Then I held up my warrant card. "Inspector Rames and Sergeant Sullivan. We're very sorry for your loss."

At my final word, Lynn's breath hitched. She lifted a tissue to dab her eyes.

"God," Jason groaned. "She's been crying all evening and all morning, and then you come and she cries more. The next thing you're going to say is that you want to ask us some questions, and then she'll cry again. Well, you can bugger off, because I've just had the worst news of my life and I want to be alone."

He left the room.

Lynn snivelled and sat up straighter, fixing her brown eyes on us. "S-sorry."

"It's okay," I said. "He got it right. We would like to ask you some questions, if you can handle it now."

"I'd like to get it over with."

"Okay, then." I sat down beside her. "Just for the record, you're Lynn Castle-Ackerman, Zoe's half-sister? And you live here?"

Fresh tears flowed. "Yes. I go to Socrico University, but I'm a home student."

Socrico University was the educational institution of the highest prestige outside New London. Those who didn't pass everything with flying colours didn't make the cut.

"Where are your parents?"

"On their way back."

"Okay. When did you last see Zoe?"

"She was here last night. We all had dinner together."

"I understand that she argued with Maxx and left alone soon afterwards?"

Lynn worried her lip. "Yes."

"Do you know what they argued about?"

"No. I was in my room by then, getting ready to go out. I just heard the shouting. But the scandal has always been hard on them, so it often raises tensions."

"Because they're step-siblings?" I clarified.

"Yes. Maxx is my half-brother."

Alex, still standing, cut in. "You said you were getting ready to go out. Where were you going?"

"Oh..." She pressed the tissue against her eyes. "I was supposed to be meeting my boyfriend at The Silver Star. But he messaged me while I was riding the tram there to break up."

"I'm sorry," I said. It was odd to offer my condolences for anything other than death. "So you came back?"

"Yes...I stayed on the tram until it came back."

"Did you go anywhere near Terra Road?"

"No. Why -- oh, God." She stared at us. "Is that where...?"

"Yes. Zoe was murdered near Ryker James' workshop. Do you know why she might have been there?"

Lynn furrowed her brow. "She once said to me that when they were together, they'd walk around in the dark as if they were in a garden. She found it calming."

"They walked around the backstreets and the alleyways?" Alex sounded incredulous.

"Yes. She was safe with Ryker."

"Did she spend much time with him after she married Maxx?" I asked.

"I don't know. I don't think so. She never really spoke about him."

"How did she seem in the past few days? Was she her usual self?"

Lynn nodded, sniffling.

"Did she have any enemies? Anyone who might have wanted to hurt her?"

"No. I can't believe someone would do this..."

Dress shoes tapped down the hallway, and a man vaguely resembling Zoe appeared in the entrance to the living space. He took one look at us and frowned.

I stood up. "Daniel Castle?"

"Yes." His voice was a monotone, like he thought he might be dreaming. "Are you the police?"

"Yes, sir. We're here to ask you some questions about Zoe."

His eyes turned glassy. "Zoe... I suppose you'd better come to my office."

The office was upstairs, and we rode a lift up the extremely short distance from the ground floor of the duplex to the first. Daniel showed us into a room that seemed as if it was exactly what the enigmatic squid-worm skyscraper had been made for. The whole space was like a robotic convention, filled with so many parts and machines that the glare of the lights shining off everything at once momentarily blinded me. I squinted at robots with wings, wheeled legs, and two heads through watering eyes. What the...?

They were all deactivated, some of them frozen in odd positions, and scattered throughout the room. A couple had their backs open as if someone had recently been in the middle of adjusting something within them, and workbenches made from sheets of glass so thin that they were almost invisible stood near the back of the space. A desk and a couple of sofas were clustered near it, and that was where Elena Ackerman was waiting for us.

The CEO of Ackerman Electronics was middle-aged but wearing it well: she had a heart-shaped face framed by blonde hair; small, pink lips; and fair, smooth skin that was dusted with freckles like stars. But any softness this might have suggested was stolen by her eyes, which were steel blue and just as hard as the metal.

I introduced myself and Alex, and then we all sat down.

"I'm very sorry for your loss," I said. "Formal statements will be taken soon, but I was hoping to ask a few quick questions to help the investigation into Zoe's death."

Elena shrugged. Daniel slumped in his chair.

"Zoe was here with Maxx yesterday evening, wasn't she?"

"Yes, and Harley," Elena said. "They came for a family meal. That was the last time we saw her."

"She and Maxx fought."

"Couples fight."

"Do you know what they were arguing about?"

"We'd disbanded," Daniel said thickly. "They were still in the dining room. I only heard raised voices." He glanced at his wife.

"Yes, it was white noise," she said.

"What happened after that?" Alex asked.

Elena shrugged one delicate shoulder. "Zoe left. Maxx left with Harley a few minutes later. Lynn and Jason went out."

"What did you do?"

"I went out soon after, just down to the botanical garden for a walk. I probably stayed there for an hour, unwinding. Then I came back up to our office."

I looked at Daniel.

"I remained in the office while Elena was gone."

"Did you see anyone in the garden while you were down there, Mrs Ackerman?" I asked.

"It was empty. No one takes advantage of it like I do in the winter."

I thought she'd be right at home among the frosted vegetation. "So you were both alone between half eight and half nine?"

"Yes."

I exchanged a glance with Alex.

"What was your relationship like with Zoe?" he asked.

Both Castle-Ackermans hesitated. Zoe had been Daniel's biological child with a woman who'd died not long after her birth, but Elena hadn't been related to her at all.

"I love her," Daniel said eventually, his voice hoarse. "We are...we were...very close. She was my pride and joy."

"But she didn't like me," his wife added coldly. "And I didn't like her. We never wasted our time fighting: we were civil, and we stayed out of each other's way. Whether she lived or died was of no concern to me."

"Elena!" Daniel's face darkened.

"They have to understand. I didn't hate her -- I just disliked her. I could always tell she loved Maxx as more than a step-brother. Now look at the ruin she's brought on us. You know our sales have been falling since they married! Our name has become a dirty word."

I cleared my throat. "Did Zoe have any real enemies, then?"

"No." Daniel's voice trembled. "Everyone loved her."

"What about Ryker James?"

"They should have married instead," Elena muttered. "They almost did."

"After she jilted Ryker, what were her relations like with him?"

Elena's lips thinned. "We heard no more of him."

"Yes," Daniel said. "In fact, he hasn't been mentioned in this household since."

I looked at Alex again. He looked back at me. We'd hit a dead end.

"Thank you for your time." I stood up. "That's everything for now. If you think of anything else that could help the investigation, you can contact us through our Xplora page."

Like the oldest son, they left us to find our own way out. We said nothing as we took the lift back to their ground floor, and nothing until we were out the front door and had shut it properly. Then Alex addressed what I'd been thinking. "No one has a solid alibi."

"No." I dragged a hand through my hair. "Damn it. We'll go back to the station -- "

The lift doors flew open at the other end of the hallway. A girl roughly the same age as Lynn and Jason stepped out, baby-faced but heavily made up, her curly hair dyed rose-gold.

She ignored the PRB standing guard and rang the doorbell of the Castle-Ackerman flat. Before I could ask what she was doing, the camera recognised her and granted automatic access. She went inside and slammed the door, locking us out for good.

I stared. "Who the fuck was that?"