"You know what Herdstones are?" Lord Magister Luuk says after you enter the tower, not looking up from the battered kettle he was patiently watching.
"Gathering points for the Beastmen," you say. They'd come up a time or two in Regimand's travels.
"They're also the complete opposite of Waystones, which scares the shit out of anyone with sense." He scratches at his shoulder, where the angry red of a new scar is visible under his leathers. "If you can interrupt them while they're setting one up, and drag the thing away before they summon reinforcements, you've got a menhir attuned to Ghur but not yet tainted by their rituals. It was a stroke of luck to find one just as you asked for this." You suppress a smile. "I carved out a recess in the side of this one, and you need to fill it with heart-blood of wild animals spilled by the blade I left in it, that's the 'key' you asked for. Wild, mind - nothing domesticated. Once it's full, the chosen subject drinks it, and as long as they drink most of it the transformation should take hold. Tea?"