A tear in reality has opened on the contested world, and the brotherhood has come to seal it — alone, against a foe that has every advantage of numbers.
ATTACKER AND DEFENDER The Grey Knights are the defender: the vigil, a tiny brotherhood holding a warp-breach or consecration site against the tide. The opposing gang is the attacker: it means to out-body the brotherhood, force the trade the few cannot afford, and overrun the breach before the ritual completes.
BATTLEFIELD Set up a central objective marking the warp-breach, with scattered ruins and cover across the board. The ground immediately around the breach is open, offering the defender little to hide behind and the attacker no easy approach.
DEPLOYMENT The Grey Knights deploy first, arrayed around the central breach. The attacker then deploys along the board edges with its superior numbers, ready to advance and overwhelm the site from every side.
THE CONSECRATION RITUAL From the first round the Grey Knights are sealing the breach. So long as a Grey Knight remains within Short of the objective and it is not contested by an enemy, the ritual advances one step each round; the brotherhood's goal is to hold it unbroken to the end of the game.
ENDING THE BATTLE The battle ends at the close of the agreed number of rounds, or immediately if the brotherhood is reduced to two or fewer standing fighters.
VICTORY The Grey Knights win if they still control the breach at the end of the game with the Grand Master or a Champion standing. The attacker wins if it holds the breach at game's end, or if it reduces the brotherhood to two or fewer standing fighters.
REWARDS The Grey Knights gain renown scaled to how many brothers survived the vigil, within the campaign cap, feeding the unbroken-brotherhood sub-plot. The attacker gains a reward for breaking the vigil, or for each Grey Knight it out-bodied off the board.
CONTROL TRACK A Grey Knights win holds the Control-Track marker on the world as the breach is sealed. An attacker win pushes the marker toward the attacker, the warp left open where the brotherhood could not hold.
TACTICS The brotherhood cannot win a numbers game, so it must make the ground itself a weapon: raise Sanctuary over the breach, cluster tight to keep the Aegis dense, and trust the Nemesis blades to punish every foe that commits to the charge. The attacker must accept losses to force the trade — swamp the site from more angles than the few can hold, and spend bodies to take veterans the brotherhood cannot replace.