Lacra wants to discuss a mysterious matter with me – supposedly, she knows of something more that could help our fight against Brencis.
Follow the wisps from the shrine to the hidden cave
After Our Rotten Roots, speak with Lacra and choose “You had some idea to talk through?” to begin this expedition. Follow the swamp path to the roadside shrine, then follow the wisps to a stone slab and inspect it.
Stay with the wisps through the zombie and tatzelwurm encounters. In the ravine’s vine-covered clearing, inspect the severed arm and finish examining its clues to receive The Relic of St. Tobias. This happens outdoors, before the crypt entrance.
After the hellhound fight, follow the wisps to the rock wall covered in red roots. Interact with the root mass to open the crypt. Inside, follow the passage to the gap and use Shadowstep to reach the corpse holding The Vrakhir.
Continue to the sarcophagus encounter. After the fight, Lacra opens the wall into a hidden cave, where she finds the mandrake. Accepting her offer grants Mandrake Ward. The later conversation contains the optional romance and the blood choice associated with Mesmerise; use the linked guides for those choices and their rewards.