According to Bethesda's Japanese website for the game, The Evil Within will be built using id Tech 5 engine.
The Evil Within is designed by Shinji Mikami, the creative mind behind the original Resident Evil. The game revolves around Detective Sebastian and his partner who are summoned to a mass murder crime scene to find a "powerful, mysterious force lying in wait."
Sebastian, along with the whole police force at the crime scene, is attacked and loses consciousness. When he wakes, he finds that the word around him is inhabited by monsters. To figure out what happened and to find a way out, Sebastian must face his own fears.
The influence of Shinji Mikami's Resident Evil roots is quite evident in the game's atmosphere and gameplay in which"players must survive on limited resources, experiencing that supreme match of action and horror, that indescribable terror. To survive in an afflicted world, your anxiety and nerves will be pushed to the edge."