After the defeat of the mystic Memnan Saa, the Bureau for Paranormal Research and Defense -- on the outs with the United States government after the bloodstained rescue of Liz Sherman -- embarks to the Ural Mountains, the site of B.P.R.D.: Hollow Earth, to put the frog menace to rest once and for all. Meanwhile, Kate Corrigan heads to Hunte Castle in Austria, where Hellboy killed the Conqueror Worm, on her own rescue mission -- to save ectoplasmic special agent Johann Kraus, possessed by the ghost of Lobster Johnson.