‘Sister!’ Haskia bellows, as the Heretic Astartes steps forward and takes hold of Veridia by the throat, lifting her from her feet. I see Veridia’s hand move as she frees a promethium charge from her belt and primes it, before driving it straight through the heretic’s eye-lens. It detonates immediately, fire blooming out in a bright, terrible instant. The traitor’s armour squeals and crumples, and then both it and Veridia are consumed.

Immolated.

‘Sister!’ Haskia shouts again.

She turns and fires on the closest of the heretics until her bolter empties and she draws her sword in its place. Haskia cleaves to and fro, cutting through armour and spilling dust, her pale face set with rage. She is so intent on vengeance, on reaching what remains of Veridia, that she does not take cover when the heretics fire on her. The ensorcelled shells blast Haskia backwards, burning. She lands on her back on the floor, her armour shattered and her skin smouldering. She tries to rise, but she cannot.

I hesitate, just for a heartbeat.

‘Keep going,’ Sarita rasps to me as we fight. She is struggling to breathe now, too. She wavers on her feet, her skin slicked with sweat. ‘I will go to her.’

‘Not alone, you won’t,’ Munari says, as she fires her bolter one-handed. ‘I told you, this is a story for both of us.’

‘Stay together,’ I tell them. ‘I want to hear you tell it when it is done. Both of you.’

They nod to me, and then we separate. The twins disappear amongst the heretics while I turn to the storm and the stairway, my eyes fixed on what lies ahead.

‘We go onwards!’ I shout to the others as we push our way through the last of the sorcerer’s silent brothers. To the foot of the crystal stairs, and the edge of the storm. It is a thick swathe of cloud now. A wallowing thunderhead, bristling with lightning.

‘How will we get through?’ Ravara shouts, over the roar of it.

I look at the storm. At the roiling clouds that tumble over one another like serpents. At the tiny light, flickering in its depths. My eyes fall to the sword in my hand. To the words, inscribed along the length of the blade.

‘We cut our way through,’ I say.

I raise my sword, and stride towards the storm. Lightning arcs all around me, cracking marble and shattering stone. The clouds roar and twist into the shapes of wrathful faces. They scream.

But they cannot stop me.