Artie fills the gang in: because Paracelsus is taking precedence as Caretaker over Mrs. Frederic, he must be taken alive in order not to cause her any further harm. Now to figure out where in the world he is...
The DNA sample that Artie used to save Claudia was not from Joshua, which Steve picks up on, but doesn't understand why Artie's lying.
Claudia is on the warpath for Para-freaking-celsus, and finds a man matching his description curing patients. Curing? You never know with this guy. Pete rushes off on his own, claiming that Myka has to stay behind for her oncologist appointment, and she counters by saying it's not til the end of the week - she can save the world, like, three times by then. Off they go to San Francisco to catch a crook.
Sutton tries to apologize to Nick for not being there, for immortalizing them, and for not jumping between Charlotte and a bullet. Nick is furious and wishes his father were dead, then runs off. Claudia talks some manners into him and gets him to describe Paracelsus' lab - turns out, it was covered in petrified wood...
Which is what Myka and Pete find out when they visit one of the patients cured by Paracelsus, who says he said something about air turning to stone. They piece it together and realize Paracelsus is after the petrified wood in Coit Tower, a San Francisco landmark, where he plans to immortalize himself. But Sutton, wanting to take revenge on his brother, shows up and aims a gun at the man, ruining their plan. Pete catches up with him, and transports him back to where he belongs.
Although Nick is mad at his father for his hero move, it opens up a discussion between them. They resolve their issues and the Regents assign them a new, and mortal, life.
With the immortals wrapped up and Paracelsus on his way to the bronzer, Myka slips away as quietly as possible to the hospital, where her doctor plans to remove the cancerous mass in her body. She's strong for Pete, but breaks down when she's alone. Mrs. Frederic continues to worsen, and since Paracelsus - who ingested chemicals that prevent him from being bronzed - knows how to save her, Pete decides to have a man-to-man with the baddie.
Paracelsus warns Pete that the woman he should be afraid of losing is not Mrs. Frederic, but Myka, who's more ill than anyone knows. Pete is furious, but Paracelsus keeps his cool and manipulates Pete into believing that he can save Myka if Pete will just make him mortal and erase his mind before he's bronzed. With careful trickery, Paracelsus gets Pete to make his connection to the Warehouse stronger.
Steve confronts Artie on his lie, and Mrs. Frederic urges him to tell Claudia the truth - that her sister, Claire, is alive, and a very dangerous woman. Claudia is outraged, but given that there's a monster on the loose, she has to shelve the heart-to-heart for now. She saves Mrs. Frederic by disconnecting her from the Warehouse, and takes her place. They realize that Paracelsus now has complete control of the Warehouse, and must get some distance between themselves and him.
But Claudia can't go! She realizes, in that uncanny Caretaker way, that the Warehouse needs her - and that it will protect her. She must fight him from inside the Warehouse, while they fight from without. With the briefest and most heartfelt of goodbyes, the agents leave and are locked out, while Claudia goes to find her nemesis.