Spoilers for one of the Ghost Legion subplots, if you haven't already go read it it's alot of fun.
Context: Gavran, Morten, and Sorry are all Savlar Chem-Dogs, Drass is an Adamus Assassin disguised as a Chem-Dog, Qope Halver and Sokrate are Headhunters hunting Drass.
> ‘Ready?’ Drass said, and Gavran found himself nodding alongside Morten and Sorry. ‘If this doesn’t work, know that you’ll die having done the Emperor’s work.’
> He loped away, fast and silent, another shadow in the night. Gavran watched him go, his heart in his throat. Beside him, Morten propped the plasma gun on the top of the wall, and flicked the power switch to maximal.
> ‘You’re supposed to wait–’ Sorry began.
> Morten fired.
> The incandescent bolt of energy streaked out into the night. It seared into Gavran’s night vision, but not before it brought him the image of Drass falling, a hole blown right through his torso.
> ‘What–’
> Sorry was gasping, bubbling, the sound of a man choking on his own blood. Gavran was still blinking away the spots, trying to make sense of what was happening, when he felt the touch of a wet blade against his own throat.
> ‘Sorry, Gavran,’ Morten whispered. ‘But I did tell you that I weren’t always a Chem-Dog.’
> ‘Hydra Dominatus! Hydra Dominatus!’
> Qope Halver had raised his Stalker-pattern boltgun as soon as the plasma bolt flashed out into the night. His helmet’s night-vision setting registered the downed body, killed instantly, and he saw the distinctive pistol and mask hanging at the belt – the tools of the Assassin they’d been trailing, although he’d picked up some new clothes from somewhere.
> He hadn’t expected the short human in the uniform of the enemy, advancing down the middle of the street with her hands raised and repeating the war cry of his Legion.
> ‘What in the primarch’s name is this?’ muttered Sokrate, beside him.
> ‘No idea,’ Halver admitted. ‘Let’s find out.’
> He covered the human as she approached, then held up one hand when she got to thirty feet away. ‘That’s far enough. Who are you?’
> ‘Morten Shanell, lord,’ the human replied. She was sweating with nerves, but also, so far as Halver was any judge of mortal emotions, with excitement. ‘I was recruited into the Legion ten years ago, by an operative named Hojun Frale. He gave me a code word. I was waiting for activation, but when I learned that we were fighting the Legion…’ She shrugged. ‘I had to act. That man was an Imperial Assassin.’
> Halver grunted. ‘What was your code word?’
> ‘Haplocke, my lord.’
> Halver looked at Sokrate. ‘Mean anything to you?’
> ‘No.’
> ‘Me neither.’ Halver pulled the trigger, and Morten’s. head exploded. He activated his vox. ‘Harrowmaster. Mission accomplished.’