Faith had no idea just what the hell was going on. She recognized the designs Castiel had drawn as Devil's Traps symbols, which meant Castiel was trapping his girlfriend. He'd been the last of them to still trust Ruby, and that fact alone was enough to put Faith immediately on edge.
She was sitting on the floor of the warehouse, her back against the wall as she watched, silently.
Castiel said he was sorry.
Ruby asked how, Faith guessed how they knew.
Not that Faith even knew for sure what they knew.
Until Castiel explained. Faith raised her head to look first at the angel and then at Sam, Ruby just beyond that. Blood. Drinking her blood.
Her face remained impassive as she slowly and calmly stood up, walking at a steady pace out of the warehouse.