‘So how does this work?’

They’d finished the op six hours ago. Left the Oltanis system four. And as the Blackbird thundered through space towards the Lliew Rift, deeper and further rimward into the Neutral Zone, they still knew little more about what came next but their destination.

None of them could sleep, and by now, Rosewood, Nallera, and Q’ira had camped out in the lounge. Nallera had found a sports game to put on, and it spoke of Rosewood’s desperation for distraction that he was tolerating watching lower-league Parisses Squares games.

He looked at Q’ira at her question. ‘Falling off the ramp loses points -’

‘I mean the job. I don’t care about the rules of the game. They’re just hitting each other with sticks.’ She waved a hand at the door. ‘Do we sit around and do nothing until Aryn bursts out saying he’s got it?’ It hadn’t taken Falaris long to decrypt the data they’d pulled off Kanem’s console. Since then, Aryn had been locked in his room, studying whatever it was that the Changeling had needed Kanem’s people’s hardware and expertise for.

‘You know, this is my first time with this,’ Rosewood admitted, looking at Nallera.

‘Whash?’ Her eyes had been on the game. She swallowed a mouthful of chips before sheepishly extending the bag to them. ‘You want some?’

‘I mean – yes, but – Mac. Does he just burst out yelling “Eureka?”’ Rosewood grabbed a fistful of chips.

‘Basically. We just gotta wait.’

Q’ira leaned over to pluck a single chip from the bag. ‘What is this Lliew Rift?’

‘It’s what happens when Romulan scientists fuck up their development of the singularity core centuries ago,’ said Rosewood, leaning back in his chair and watching the game on the holo-projector. ‘Now you’ve got a whole stretch of space full of subspace distortions. Nobody knows much about it; the Star Empire stuck the region in the Neutral Zone after the Earth-Romulan War, and it’s such a hellscape of stellar phenomena that nobody’s gone near it since the collapse.’

‘Weird place for a Changeling to run,’ sighed Q’ira.

Aryn didn’t yell ‘Eureka’ – or, indeed, anything at all – once he’d finished. He did burst into the lounge, wild-haired and wild-eyed, his Daystrom Institute t-shirt coffee-stained and rumpled. What he lacked in yelling he made up for with hissing intensity as he advanced on them, brandishing a PADD. ‘Time travel.’

They stared at him. Nallera was first to react, throwing down the bag of chips. ‘Fuck’s sake. Get Cassidy.’

Cassidy looked like he, at least, had been sleeping, and rubbed his eyes as he entered the lounge. ‘This better be what you know, and not what you’ve guessed, Aryn,’ he growled.

‘Well, I can’t be sure,’ Aryn babbled. He’d probably had too much coffee. ‘But this is my best working theory, based on both the information from the server and the chosen destination -’

‘Maybe try skipping to the end,’ Rosewood suggested gently.

‘Yes!’ Aryn snapped his fingers. ‘The Kairos Regulator was originally…’

‘Is this the end?’ Nallera muttered. Rosewood elbowed her.

‘…a high-energy particle device used for controlled manipulations of subspace. It entered life as something fairly benign – not a weapon, but for precise calibrations in advanced scientific studies. Obviously it then took a different form at Daystrom Station -’

‘I want Aestri’s plan, not the device’s life history,’ Cassidy snapped.

‘Right.’ Aryn slowed down. Once again he called up a holographic pen, relying on the projectors to let him write explanations in mid-air as he carried on. ‘Aestri called on Kanem’s R&D people – annoyingly they were probably home, asleep, far away when we hit the facility – to modify the device in accordance with her specifications. She didn’t really explain why, so I have some of their theories in the notes, and my own extrapolations. What is clear is that the Borg tech they integrated into the Regulator allows it to manipulate gravimetric distortions far beyond its original design. Specifically… they integrated a vinculum.’

Rosewood’s eyebrows hit his hairline. ‘A vinculum – are you kidding? They had one?’

‘The remains of one. In sufficient condition to serve the purpose Aestri needed: to process subspace signals and feedback on a massive scale.’ Aryn pressed a button on his PADD and a 3D rendering of the modified Regulator flickered to life from the holographic projector. Aryn zoomed in on its core components. ‘The vinculum enables to Regulator to generate much larger gravimetric pulses that can create artificial tears in the fabric of space-time. Ones the Regulator is capable of calibrating.’

‘So, like, a wormhole,’ said Nallera.

‘That’s space. What does the Regulator affect? Time. Time-wormhole.’

‘Shit,’ surmised Rosewood. ‘Why the Lliew Rift, then?’

‘The Regulator can already do that. But the power to do it would be… massive.’ Aryn blinked as he mentally ran calculations, then clearly decided to not burden them with the details. ‘But the Rift is rife with subspace distortions. If the Changeling can identify the right kind of rift in space-time, then amplify and calibrate it with the Regulator, it doesn’t need that power boost.’

Nallera raised a finger. ‘That sounds like something that could go very wrong.’

‘Absolutely. If the wormhole destabilises or collapsed prematurely, it could cause a masssive subspace shockwave. If she succeeds, she travels in time to… who knows when. If she fails, she could tear apart local space-time.’

Silence met his words. Q’ira’s nose wrinkled. ‘…why does she wanna time travel?’

‘Go back to Frontier Day, make sure the Borg plan succeeds,’ rumbled Cassidy. ‘Go back to the Dominion War, tell them how to beat us.’

‘Or to leave the Alpha Quadrant alone,’ Aryn said. ‘The Founders care about nothing more than themselves and their own wellbeing. They run the Dominion to control what they fear: everything.’

‘No Dominion War at all sounds like a peach,’ said Cassidy, hands on hips, ‘but I don’t want to face the paperwork of failing to stop a time travelling Changeling.’

‘But if the war didn’t happen, we’d -’

‘Nope.’ Rosewood raised a sharp hand to cut Aryn off. ‘No Grandfather Paradox talk. Absolutely not.’

Nallera looked between Aryn and Cassidy. ‘What does this mean for the mission? We hunt down her ship, stop her, save the day?’

Aryn shook his head. ‘I expect she’ll have to board this research facility at the edge of the Rift. She’ll need its core to power the Regulator.’

‘That buys us time, even though she’s ahead of us,’ said Nallera. ‘No way that facility’s going to be working properly, and even if it is, you don’t just plug in a device like that to a singularity core. It’ll take modifying.’

‘So we board the station,’ said Q’ira, sitting up. ‘Take out any goons she’s got, capture her, and prove to the galaxy that she’s a Changeling.’

The simplicity of it had Rosewood take a sharp breath and look at Cassidy, whose granite brow was folded like his face had been carved that way from stone. After a beat, he looked at Aryn and said, ‘How do we stop this?’

Aryn clicked his tongue. ‘The obvious way is to prevent her from powering up the Regulator in the first place. Once the process starts… there’s literally no telling how quick it will be. It’s very dependent on localised subspace distortions in the Rift. Off the top of my head, you’d probably want some sort of directed tetryon beam that could stop the process or close any wormhole.’

‘Like the sort of thing the Cardassians did with Underspace,’ surmised Rosewood.

‘So, Starfleet science rays.’ Q’ira waved a hand. ‘Blackbird can do that, right?’

Aryn ran a hand through his hair and looked at Nallera. ‘I suppose we get to work on that, then, Nal?’

‘Do it,’ agreed Cassidy. ‘If we can get to the Changeling before it rips up space-time or ruins history, so much the better. But we better have a Plan B. You’ve got less than twelve hours.’

‘Then I,’ said Q’ira, sticking her nose in the air as she stood, ‘am going to get some beauty-sleep. One has to look gorgeous for a vengeance spree.’

Rosewood stayed put as the other three left, eyes locked on Cassidy. He waited until they were gone before he sat up and said, ‘Blackbird isn’t the kind of ship you send to shut a crazy time-wormhole or stop a subspace eruption.’

‘No.’ Cassidy worked his jaw. ‘We are who you send to stop a Changeling starting any of that shit in the first place. But you’re right. We need a Plan C.’

‘What I want is to board that station. Find the Changeling. And not just melt it with… I don’t know what you use to melt Changelings. But get it to tell me all of its secrets first. Like what it did with Tiran. What they did with everyone.’

A beat. Then Cassidy gave a sharp nod. ‘I worked with her for fifteen years,’ he said, glowering at nothing in particular. ‘But let’s be real. She’s probably dead. And there’s probably no way we ever learn when we lost her. Maybe you never even met her.’ He rubbed his temple. ‘Damned thing is she’s the person who’d tell me what I gotta do next.’

It was the closest thing to uncertainty Rosewood had ever seen Cassidy express. A day ago, he would have sneered, exploited it. Standing in the dark in the chop shop office over Kanem’s corpse had made everything different. ‘How the hell do you stop the fury from blinding you?’

‘Practice,’ Cassidy said, sharper this time. ‘Not practice in controlling anger. Practice in trusting your gut when you’re not blind. You can rationalise a billion atrocities; it’s your instincts that make you know right from wrong. So you practice listening to ‘em, so when it matters, really matters, you can tell the difference between them and… anything compromising.’ He took a deep breath and straightened. ‘You also gotta be less afraid of being wrong. Because you will be wrong, sometimes. Because this galaxy doesn’t just make it difficult to be right – sometimes, it’s downright impossible.’

‘And until you’ve got that practice down?’ Rosewood swallowed. ‘Here? In the dark?’

Cassidy didn’t smile. But his grimace held a certain wryness as he looked over. ‘Simple. Stand by the team.’