They're both on Amazon:
The Kindle versions are both like $7 but I recommend both, especially Book of Dark Knight. It gets really gritty in certain scenes, especially between Itachi and Yashiro.
Itachi. Its always Itachi.
Sorry it took so long to reply. I haven't been logged in for a while. If you'd like to read more, here are the two light novels where I gained most of my information. It goes into the details of the coup and the various character motivations during that time period:
https://www.amazon.com/Naruto-Itachis-Story-Vol-Daylight/dp/1421591308
https://www.amazon.com/Naruto-Itachis-Story-Vol-Midnight/dp/1421591316