Star Wars: Lords of the Sith is a Star Wars novel by Paul S. Kemp, published in April 2015. Set between the film Revenge of the Sith and the novel Star Wars: Tarkin, it features Darth Vader and Emperor Palpatine facing off against revolutionaries. Lords of the Sith was one of the first four novels published in the franchise after Lucasfilm redefined Star Wars continuity in April 2014, and is considered Canon.
The story occurs in a relatively short time span which I thought would be a problem at first, but upon completion I loved it. Star Wars: Lords of the Sith shows Darth Vader at the height of his power, and ferocity. It also explores the delicate relationship he has with Emperor Palpatine.
The story is centered around the Free Ryloth Movement lead by Cham Syndulla (father of Hera Syndulla one of the main characters in Star Wars: Rebels). The movement is at first focused only on Ryloth, but at the end becomes the beginning of the Galactic Resistance.
The character that I fell in love with is Isval, the female Twi'lek, who is Cham's right hand person. Isval is an amazingly complex character full of passion, love, and anger.
I highly recommend you give Star Wars: Lords of the Sith a read. You will not be disappointed.