Originally written as one of about 20 short fics I wrote during NaNoWriMo 2013 (when I went on a Divergent kick for about a week), this has been sitting in my to-finish-and-post folder for three months until today I finally got sick of having it lying around incomplete. I may come back and polish it later.

I just... really love these two characters.

'What's that?'

Caleb jerks in shock, the hand holding the needle missing the test tube in his other hand, a few blue drops splattering on the metallic surface of the table. He looks around to see a boy behind him, dressed in the black of the Dauntless, with a blue armband that shows loyalty to Erudite.

And then he recognises the boy wearing the clothes, his green eyes glinting with amusement.

Peter.

'You!' Caleb says. His mouth feels dry. 'You – what are you doing in here?'

Peter smirks. 'I could ask you the same thing, Stiff.' Casually, like he has any right to be here, Peter strolls over and leans back against the bench, his elbow far too close to a bottle of acid for Caleb's liking. 'Aren't you meant to be helping your sister with... the resistance, or whatever the hell she's doing these days?'

Caleb lowers the needle and places the test tube in a rack; his gaze flits from Peter's face to the bottle. 'Don't lean there,' he says.

Peter pauses, looks over his shoulder. 'Huh.' He draws his arm away, then turns and bends down to read the label. 'Highly concentrated hydrochloric acid.' He looks back up and raises an eyebrow at Caleb. 'Don't know what they're doing, entrusting a kid with that.'

Caleb shoots him a look, his hands stiffly held by his sides. 'I'm the same age as you, and I'm plenty trustworthy with these chemicals. You, on the other hand,' and he leans forward and carefully snatches the bottle away, 'I don't think should be anywhere near them.'

Peter rolls his eyes, straightening up. 'Whatever. You didn't answer my question.'

'And you didn't answer mine,' says Caleb, carefully putting the bottle aside.

'It's pretty obvious, isn't it?' Peter lifts his arm with the blue armband. 'What else could I be doing here?'

'That's not what I meant.' Caleb eyes Peter suspiciously. 'You're not meant to be in the labs.'

'True.' Peter goes back to leaning against the bench. 'Gonna do anything about it?'

Caleb's torn between wariness and irritation. This is his lab. Peter has no right to be in here. But he also knows that Peter could kill him with one hand.

In the end, wariness wins out. 'Whatever,' he mutters.

He turns away, and picks up the needle again.

'You still didn't answer my question, Stiff,' Peter points out, and Caleb makes a noise of frustration.

'Which one would that be, again?' He's really starting to lose track of their conversation. Peter unsettles him. And being unsettled makes him irritated, because he's meant to always be calm and collected.

'I asked, what's that?' Peter repeats.

'It's a paralytic serum that imitates death,' Caleb snaps. 'Right now it's in its early stages and happens to be highly volatile so I would greatly appreciate it if you didn't interrupt me.'

Peter is silent after this, which is somehow just as unsettling as the chatter. Caleb tries to focus anyway. Once the syringe of blue liquid is injected into the test tube, he places the needle on the bench and gently swirls the tube with his other hand. As they watch, the cloudy blue colour fades away, until the serum turns clear.

Peter whistles. 'That's pretty cool. How'd it do that?'

Caleb glances at him, placing the test tube safely into the rack. 'Trace amount of a substance that you wouldn't remember if I tried to say,' he says curtly. 'Was that everything?'

Peter ignores this, and leans forward for a better look. 'Paralytic, huh. You said it replicates death?'

Caleb hesitates, then nods, and grudgingly elaborates. 'One dose of this makes the subject immobile for a temporary amount of time.' He feels himself start to calm as he explains, knows he can't keep the enthusiasm out of his voice. 'They're in full consciousness, but exhibit no vital signs. Not even a pulse.'

'That's pretty neat,' Peter says lightly, then straightens up again, and fixes Caleb with a piercing stare that makes him feel suddenly uncomfortable, like Peter's looking into his brain.

'What?' he says, his hands going into the pockets of his lab coat. It's difficult to get a read on Peter, and the feeling of calm is gone again. He can't help that the question comes out more aggressively than it probably should. 'What is it?'

Peter stares at him, then his mouth twitches in a smile. 'It was all a front, wasn't it?'

Caleb stares at him.

'At Amity.' Caleb doesn't like the smug, satisfied, knowing look in Peter's eyes; it feels like trouble. 'The whole, sibling banter, sharing secrets, trusting each other. You were always planning to come back here, weren't you?' Peter's eyes are sharp like a hawk's.

Caleb is very still. Then, he looks away with a shrug.

He keeps his expression as neutral as he can, but out of the corner of his eye, he can see Peter's smirk widen. He knows that Peter isn't fooled, that his silence gives him away better than anything he could say.

He glances over as Peter laughs, and though it is clearly genuine, it's not a pleasant sound, more sardonic than amused, and it grates over Caleb's ears like a fork on metal. 'Don't look so guilty,' Peter calls to him in a mocking false reassurance, as he walks backwards towards the exit of the lab. 'We're on the same side here, remember?'

'Yeah,' says Caleb, as the door slides shut, but he can't help but feel that if he and Peter are on the same side then he's not sure this is the right side after all.