In the Depths of Hades

On Armageddon, the Marines Malevolent want to lead an all-out assault on the orks infesting the ruins of Hades Hive. But to do so they will need numbers, and their Astra Militarum allies are unwilling to threaten the lives of prisoners held by the greenskins. Embarking on a stealth mission to rescue the prisoners, how far will the Marines Malevolent go to achieve their goal?