 After delivering Cavador to Viktoria , Garrett steals a Servant mask to learn about a Mechanist technology called a " Cultivator " . Meanwhile , Karras hides inside the Mechanist cathedral in preparation for his plan . Garrett and Viktoria learn that it is the Cultivators inside Servant masks which emit red vapor , or " rust gas " . Karras had provided Servants to nobles with gardens in order to set off an apocalyptic chain reaction . Viktoria plans to lure the Servants into the hermetically sealed Mechanist cathedral before Karras activates their masks , but Garrett believes this to be too dangerous and leaves . Viktoria goes to the cathedral alone and dies while filling it with plants , and Garrett completes her plan , killing Karras in the rust gas . Afterward , Garrett is approached by a Keeper who explains that Karras ' scheme and Viktoria 's death had been prophesied . Garrett demands to know the rest of the Keepers ' prophecies as the game ends . 
