Notice that you won’t be able to progress further in Challenging and Hard difficulties than you have progressed in the Normal Story mode. You can only play a specific difficulty of a Chapter if you have completed your chosen Chapter's previous difficulty and if you have completed the previous Chapter of the same difficulty. As an example, you can only play Chapter 5 on Hard difficulty if:

• You have completed Chapter 5 on Normal and Challenging difficulties
• You have completed Chapter 4 on Hard difficulty