“The hag will get you, Rod! She comes at night and she steals children!”

Karla, ten years old and a year from starting in the forges, points at a smear of red pigment below the window casing of their time-shared hab. Ormerod, seven and small for his age, squeals in panic.

“Don’t say that! She’s not real!”

For Rod and Karla, life in the Roaches is thick with fear. They’re afraid when the gangers come calling for protection money. They’re afraid of the overseers. They’re afraid when their parents come home late from the mines. But Rod’s most afraid of the hag, the one terror they’ve never witnessed in their short lives.

“Well, that’s the hag’s sign,” says Karla, pointing.

The mark looks accidental to an adult. But the children recognise the deliberateness in the single coiling stroke and the three lines stabbing through it.

“Oh Karla, please don’t,” whimpers Rod. He imagines the long fingers which smeared it, and thinks about how close – just a few steps – the hag must have stood from where he sleeps. “Why us, Karla? What did we do?”

“You must have done it,” crows Karla. “Maybe it was stealing those caba-nuts! Maybe they were hers!”

Rod begins to moan, no no no. He was already wracked with guilt. Remembering the rapture of chewing and swallowing them makes him feel sick.

“Karla, what are we going to do?”

“Well, we can’t tell anyone because they’ll take you away for stealing.”

Karla’s wise and knows everything, and she isn’t afraid of the hag. But she delights in terrorising Rod. She can bring him to the brink of mania and then comfort him back again, because the hag doesn’t exist and Rod is a baby for thinking she does.

Early the next day, Rod goes back to the mark. Karla soothed him to sleep last night, telling him that he could leave an offering under the sign to apologise. Rod doesn’t have much beyond the clothes he wears every day, but he does have one treasure, a roughly carved plasteel figure of a Space Marine, and he’s gone out to leave it as an apology.

Karla hears his howl from the entrance of their hab, just as the family of miners who share it are returning from their shift. She runs around the corner to find Rod mutely staring at a caba-nut which has been left lying just beneath the mark.

She was joking about the nuts Rod had stolen. Could she have been right? The hag still isn’t real, Karla reminds herself, but she’s beginning to know something is very wrong. What kind of a punishment is a caba-nut? Why go to so much effort over a warren kid when whoever’s behind this could just come and beat us?

She pulls Rod away and attempts to voice a calm she doesn’t feel. “It has to be a good sign, like it means it’s all right that you swiped those nuts.”

Rod’s face loosens in trusting relief, but Karla’s mind is racing. What if they were overheard when they were talking about the hag? She glances around the alley. There are plenty of places where someone might hide and watch.

She leads Rod over to the arches, where they’ll wait out the day as usual.

A new caba-nut appears beneath the sign every day. Fears soon forgotten, Rod can’t believe his luck. He runs for the sign each morning to collect his prize while Karla feels her dread growing.

On the sixth morning she steels herself to look closer at the sign, feeling phantom eyes burning into her back as she crouches. Like all the warren kids, she can read the symbols daubed around the Roaches. There are signs of power, gang territory marks. Signs of faith, pleas to the Emperor for deliverance. Marks that set out safe places, places never go to by night, places of sickness, places of despair.

Karla wonders if the mark means another gang has moved into the neighbourhood. She feels a new twang of fear: new gangs mean more killings. But she looks closer. Gang signs are crude in a different way. Karla can’t put a finger on it, but she sees an odd passion in that red swirling stroke and its crossing lines, something beyond the everyday.

And then, on the seventh day, her fears find form.

Karla’s waiting in the archway for Rod to come over with another morning’s offering and he still hasn’t appeared. She already knows that something terrible is happening as she takes off for the alley, but it’s not like she can let him face the answer to the sign’s riddle alone.

She rounds the corner of their hab and there’s a figure standing between her and Rod, who’s backed himself against the alley wall. She can’t see its face or body, which in any case are covered by a dirty red robe. But the way it cocks its head indicates it’s aware of her arrival.

Rod’s babbling apologies; his hand is out, offering his Space Marine as penance for crimes that Karla had told him he’d committed. She feels all at once sick with herself and enraged at what this figure has forced upon them, and she runs at its back in desperate hope of giving Rod a moment to escape.

The figure is quicker than it should be. Karla feels her face brushing against the musty fringe of its robe as it steps aside, and a hard arm snaps around her torso, holding her fast. Rod’s now screaming and the figure moves swiftly towards him, taking Karla along too. She struggles but her fingers can’t get purchase on the arm, which is strangely smooth and unyielding. Now another arm is around Rod – and Karla can’t understand what she sees. A third arm is reaching for his face to stop him screaming.

She’s going to pass out. As her vision flickers, she hears a whisper of weird comfort. “Hush, child, hush.” She gazes upwards and sees its face. Eyes without pupils, teeth, and a coiling red tongue. All goes black.